Zoom lens optical system

ABSTRACT

A zoom lens having a high zoom ratio (&gt;4×) and a large aperture ratio (FNO 2.8) and capable of providing close-range focus with only a small amount of aberration fluctuations. The zoom lens comprises either five or six lens groups. An exemplary zoom lens comprises, objectwise to imagewise, a first lens group having positive refractive power, a second lens group having negative refractive power and separated from the first lens group by a first air space, a third lens group having negative refractive power and separated from the second lens group by a second air space, a fourth lens group having positive refractive power and separated from the third lens group by a third air space, and a fifth lens group having a positive refractive power and separated from said fourth lens group by a fourth air space. The zoom lens is designed such that when zooming from the maximum wide-angle state to the maximum telephoto state, at least the second lens group moves imagewise and at least one of the first lens group and said fourth lens group moves so as to increase the first and second air spaces and decrease the third and fourth air spaces. The zoom lens also satisfies one or more of a number of preferred design conditions.

FIELD OF THE INVENTION

The present invention relates to zoom lens optical systems, and moreparticularly, to such systems having a high zoom ratio and a largeaperture ratio.

BACKGROUND OF THE INVENTION

As zoom lenses having high zoom ratios and large apertures have becomemore common, there has been market demand for zoom lenses having evenlarger apertures and higher zoom ratios. Nevertheless, it has heretoforebeen impossible to realize a zoom lens based on the prior art thatsimultaneously achieves an increased aperture size while achieving ahigh zoom ratio.

Generally, zoom lenses are classified either as a positive lead type,wherein the most objectwise lens group has overall positive refractivepower (i.e., is "positive"), or as a negative lead type, wherein themost objectwise lens group has overall negative refractive power (i.e.,is "negative"). In positive lead type zoom lenses, the overall length ofthe lens is easily reduced. Accordingly, these zoom lenses are widelyused as telephoto zoom lenses. On the other hand, in negative lead typezoom lenses, the back focus is easily lengthened. Accordingly, thesezoom lenses are widely are used as wide-angle zoom lenses.

Telephoto zoom lens designs having a positive-negative-positive-positivefour-group arrangement (i.e., wherein a positive master lens group isarranged after a positive-negative-positive focal variable power system)and a positive-negative-positive-negative four-group arrangement havebeen disclosed in, for example, U.S. Pat. No. 4,673,258.

Among photographic lenses for 135-sized film format (Leica size), zoomlenses that include a focal length state wherein the focal length is 50mm are generally called standard zoom lenses. Standard zoom lens designshaving a negative-positive-negative-positive four-group arrangement havebeen disclosed in, for example, U.S. Pat. Nos. 4,591,235, 4,750,617 and4,846,562. Further, a positive-negative-positive-positive four-grouparrangement of a standard zoom lens is disclosed in U.S. Pat. No.4,439,017. Conventional positive-negative-positive-positive four-grouptype zoom lenses divide the third lens group of apositive-negative-positive three-group type zoom lens into two positivelens groups, and change the air space between the two positive lensgroups when changing the positional state of the lens (i.e., when"zooming"). It is known that this lens configuration allows thefluctuation of off-axis aberrations generated as the positional state ofthe lens changes (i.e., as the power is varied) to be satisfactorilycorrected. Accordingly, an increased zoom ratio can be realized.

With the progress in fabrication technology of aspherical lenses inrecent years, it has been possible to introduce aspherical lenses at lowcost. This has increased the number of aberration correction degrees offreedom. In addition, due to progress in fabrication technology for lensbarrels, it has become possible to control with high precision theposition of each lens group comprising a zoom lens. As a result, byincreasing the number of moveable lens groups, it has become possible tofurther increase the number of aberration correction degrees of freedom.This, in turn, has made it possible to reduce the number of lenses in azoom lens, increase zoom lens performance, and to improve theirspecifications.

In U.S. Pat. No. 5,189,557 and Japanese Patent Application Kokai No. Hei6-34885, a zoom lens is disclosed wherein an increased zoom ratio wasachieved using a positive-negative-positive-negative-positive-negativesix-group arrangement. Also, U.S. Pat. No. 5,191,476 discloses a zoomlens wherein an increased aperture size and an approximately three-foldzoom ratio were simultaneously achieved by introducing an asphericalsurface in a positive-negative-positive-positive four-group typearrangement.

In addition, Japanese Patent Application Kokai No. Hei 6-34885 disclosesa zoom lens having a positive-negative-negative-positive-positivefive-group arrangement. This zoom lens realizes an increased zoom ratioby arranging two negative lens groups imagewise of the first lens group.Furthermore, Japanese Patent Application Kokai No. Hei 8-94933 disclosesa zoom lens having a positive-negative-positive-positive four-grouparrangement that realizes an increased variable power by introducing anaspherical surface in the second lens group.

Generally, negative lead type zoom lenses are used in zoom lenses thatcover a field angle of 70° or greater. The zoom lens disclosed inJapanese Patent Application Kokai No. Hei 8-94933 is a positive leadtype zoom lens through the introduction of an aspherical surface in thesecond lens group. It satisfactorily corrects fluctuation of coma due tochanges in the field angle which tend to occur in the wide-angle state,and realizes high optical performance. However, since the second lensgroup of this zoom lens has strong negative refractive power, an attemptto increase the aperture size would greatly increase the surface areaoccupied when the on-axis light beam passes through the second lensgroup in the telephoto state (i.e., the lens positional state whereinthe focal length is longest), as compared with when the zoom lens is inthe wide-angle state (i.e., lens positional state wherein the focallength is shortest). As a result, the off-axis aberrations in thewide-angle state and the on-axis aberrations in the telephoto statecannot be simultaneously corrected. Consequently, the coexistence of anincreased aperture ratio and an increased zoom ratio is problematic.

In addition, if an attempt is made to increase the zoom ratio in anegative lead type zoom lens, the overall length of the lens in thetelephoto state tend to increase, and the on-axis light beam emittedfrom the first lens group diverges and impinges on the positive lensgroup arranged imagewise of the first lens group. Consequently, the lensdiameter tends to increase. In addition, in U.S. Pat. No. 5,499,141 (the"'141 patent"), by changing the air space between two adjacent negativelens groups when changing the lens positional state, the number ofdegrees of freedom is increased for correcting the fluctuation ofoff-axis aberrations generated as the lens positional state changes.Consequently, increased variable power and an increased opticalperformance are realized. The design in the '141 patent is such that ifthe air space between two lens groups having refractive powers of thesame sign is changed when changing the lens positional state, thefluctuation of off-axis aberrations generated as the lens positionalstate changes can be satisfactorily corrected.

Zoom lenses generally focus at close range by moving one lens group, andare broadly classified by the following three systems: front focussystems, inner focus systems, and rear focus systems. In front focussystems, control is easier during manual focusing, since the amount offocusing movement of the first lens group needed to focus on apredetermined object is nearly fixed regardless of the lens positionalstate. Nevertheless, as autofocusing has become a common function inrecent years, efforts have been made to increase its speed. To increasethe speed of the autofocus function, it is vital that the amount of workrequired to move the focusing group (i.e., weight×amount of movement) besmall. In the case of front focus systems, the lens diameter isextremely large and is thus not well-suited for autofocusing. U.S. Pat.No. 4,439,017, for example, discloses a zoom lens wherein the off-axislight beam passing through the first lens group arranged at a positionremoved from the aperture stop deviates greatly from the optical axis.Accordingly, the lens diameter of the first lens group, which is thefocusing group in the front focus system, greatly increases.

The inner focus system and the rear focus system are suited toincreasing the speed of autofocusing since a lens group having a smalllens diameter can be selected as the focusing group. For example, U.S.Pat. No. 5,499,141 discloses a zoom lens having, objectwise toimagewise, a first lens group having a positive refractive power, asecond lens group having a negative refractive power and a third lensgroup having a negative refractive power. Close-range focusing isperformed by moving the third lens group. In this zoom lens, if an innerfocus system or a rear focus system is used as to achieve close-rangefocusing, it is difficult to control the lens position of the focusinggroup, since the amount of focusing movement changes as the lenspositional state changes from the wide-angle state to the telephotostate. In particular, if the zoom ratio of the zoom lens is increased,the change in the amount of focusing movement increases greatly as thelens positional state changes. Thus, it becomes even more difficult tocontrol the lens position of the focusing group. In addition, in such azoom lens having a large aperture, fluctuations of aberrations generatedwhen focusing at close range tend to increase. Thus, it becomesdifficult to reduce the fluctuation of aberrations as the lenspositional state of the lens changes.

Further, the zoom lens disclosed in the abovementioned U.S. Pat. No.5,499,141 has a zoom ratio on the order of 3× and an FNO on the order of10 in the telephoto state, and is not suited to increasing the zoomratio and the aperture size.

SUMMARY OF THE INVENTION

The present invention relates to zoom lens optical systems, and moreparticularly, to such systems having a high zoom ratio and a largeaperture ratio. An objective of the present invention to provide aclose-range focusable variable focal length zoom lens having a high zoomratio, a large aperture ratio, and a small amount of fluctuation ofaberrations when focusing at close range. In particular, an objective ofthe present invention is to provide a variable focal length zoom lenshaving an aperture ratio on the order of substantially 1:2.8 (brightnesson the order of substantially FNO 2.8) and a zoom ratio that exceedsabout 4×.

For a zoom lens having a large aperture ratio, it is preferable toincrease the number of lenses comprising each lens group, since the needarises to correct the aberrations for each lens group. However,increasing the number of lenses results in an increased size and weightof the zoom lens barrel. This constrains the range of movement of thephotographer and has an adverse effect particularly on portability.Accordingly, maintaining the compactness of the lens system isimportant.

Thus, a first aspect of the invention is a zoom lens capable of formingan image of an object and zooming between an extreme wide-anglepositional state and an extreme telephoto positional state. The zoomlens comprises, objectwise to imagewise, a first lens group havingoverall positive refractive power, a second lens group having overallnegative refractive power and separated from the first lens group by afirst air space, a third lens group having overall negative refractivepower and separated from the second lens group by a second air space, afourth lens group having overall positive refractive power and separatedfrom the third lens group by a third air space, and a fifth lens grouphaving a positive refractive power and separated from said fourth lensgroup by a fourth air space. The zoom lens is designed such that whenzooming from the maximum wide-angle state to the maximum telephotostate, at least the second lens group moves imagewise and at least oneof the first lens group and said fourth lens group moves so as toincrease the first and second air spaces and decrease the third andfourth air spaces.

In another aspect of the invention, the second lens group has one ormore lens surfaces each with a paraxial curvature, and satisfied thedesign condition

    0.1<(Ave. C)×f.sub.w <0.6

wherein, "Ave. C" is the average value of the absolute value of theparaxial curvature of each of the one or more lens surfaces comprisingthe second lens group, and f_(w) is the focal length of the entire zoomlens in the maximum wide-angle state.

Another aspect of the invention is a zoom lens capable of forming animage of an object and zooming between an extreme wide-angle positionalstate and an extreme telephoto positional state. The zoom lenscomprises, objectwise to imagewise, a first lens group having overall apositive refractive power, a second lens group having overall negativerefractive power and separated from the first lens group by a first airspace, a third lens group having overall negative refractive power andseparated from the second lens group by a second air space, a fourthlens group having overall positive refractive power and separated fromsaid third lens group by a third air space, and a fifth lens grouphaving a positive refractive power and separated from the fourth lensgroup by a fourth air space, and a sixth lens group having a negativerefractive power and separated from the fifth lens group by a fifth airspace. The zoom lens is designed such that when zooming from the maximumwide-angle state to the maximum telephoto state, at least the secondlens group moves imagewise and the sixth lens group moves objectwise soas to increase the first and second air spaces, decrease the third andfourth air spaces, and change the fifth air space.

In a further aspect of the invention, the above zoom lens satisfies thedesign condition

    1.0<f.sub.1 /(f.sub.w ·f.sub.t).sup.1/2 <1.6

wherein f₁ is the focal length of said first lens group, f_(w) is thefocal length of the zoom lens in the maximum wide-angle state, and f_(t)is the focal length of the entire zoom lens in the maximum telephotostate.

In another aspect of the invention, the zoom lenses set forth abovepreferably satisfy a number of other design conditions, as described indetail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic optical diagram of the lens groups comprising thezoom lens of Working Examples 1-3 of the present invention, with dashedarrows depicting the movement of each lens group when zooming from theextreme wide-angle state (W) to the extreme telephoto state (T);

FIG. 2 is an optical diagram of the configuration of the zoom lensaccording to Working Example 1 of the present invention;

FIGS. 3A(I)-3A(IV) are aberration plots for spherical aberration,astigmatism, distortion and coma in the extreme wide-angle state(infinite focus) for Working Example 1;

FIGS. 3B(I)-3B(IV) are aberration plots for spherical aberration,astigmatism, distortion and coma in a first intermediate state (infinitefocus) for Working Example 1;

FIGS. 3C(I)-3C(IV) are aberration plots for spherical aberration,astigmatism, distortion and coma in a second intermediate state(infinite focus) for Working Example 1;

FIGS. 3D(I)-3D(IV) are aberration plots for spherical aberration,astigmatism, distortion and coma in the extreme telephoto state(infinite focus) for Working Example 1;

FIG. 4 is an optical diagram of the configuration of the zoom lensaccording to Working Example 2 of the present invention;

FIG. 5 is an optical diagram of the configuration of the zoom lensaccording to Working Example 3 of the present invention;

FIG. 6 is a schematic optical diagram of the lens groups comprising thezoom lens of Working Examples 4-6 of the present invention, with dashedarrows depicting the movement of each lens group when zooming from theextreme wide-angle state (W) to the extreme telephoto state (T);

FIG. 7 is an optical diagram of the configuration of the zoom lensaccording to Working Example 4 of the present invention;

FIG. 8 is an optical diagram of the configuration of the zoom lensaccording to Working Example 5 of the present invention;

FIG. 9 is an optical diagram of the configuration of the zoom lensaccording to Working Example 6 of the present invention;

FIG. 10 is a schematic optical diagram of the lens groups comprising thezoom lens of Working Examples 7-10 of the present invention, with dashedarrows depicting the movement of each lens group when zooming from theextreme wide-angle state (W) to the extreme telephoto state (T), andshowing the conditions for reducing the amount of focusing movement ofthe focusing lens group;

FIG. 11 is an optical diagram of the configuration of the zoom lensaccording to Working Example 7 of the present invention;

FIG. 12 is an optical diagram of the configuration of the zoom lensaccording to Working Example 8 of the present invention;

FIG. 13 is an optical diagram of the configuration of the zoom lensaccording to Working Example 9 of the present invention;

FIG. 14 is an optical diagram of the configuration of the zoom lensaccording to Working Example 10 of the present invention;

FIG. 15 is a schematic optical diagram of the lens groups comprising thezoom lens of Working Examples 11-13 of the present invention, withdashed arrows depicting the movement of each lens group when zoomingfrom the extreme wide-angle state (W) to the extreme telephoto state(T);

FIG. 16 is an optical diagram of the configuration of the zoom lensaccording to Working Example 11 of the present invention, with dashedarrows depicting the axial movement of the lens groups when zooming;

FIG. 17 is an optical diagram of the configuration of the zoom lensaccording to Working Example 12 of the present invention, with dashedarrows depicting the axial movement of the lens groups when zooming;

FIG. 18 is an optical diagram of the configuration of the zoom lensaccording to Working Example 13 of the present invention, with dashedarrows depicting the axial movement of the lens groups when zooming;

FIG. 19 is a schematic optical diagram of the lens groups comprising thezoom lens of Working Examples 14-16 of the present invention, withdashed arrows depicting the movement of each lens group when zoomingfrom the extreme wide-angle state (W) to the extreme telephoto state(T);

FIG. 20 is an optical diagram of the configuration of the zoom lensaccording to Working Example 14 of the present invention;

FIG. 21 is an optical diagram of the configuration of the zoom lensaccording to Working Example 15 of the present invention; and

FIG. 22 is an optical diagram of the configuration of the zoom lensaccording to Working Example 16 of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to zoom lens optical systems and moreparticularly, to such systems having a high zoom ratio and a largeaperture ratio. An objective of the present invention is to provide azoom lens having a large aperture ratio on the order of substantially1:2.8 (i.e., brightness on the order of substantially FNO 2.8) and azoom ratio in excess of about 4×. Another objective of the presentinvention to provide a high-aperture-ratio, high-zoom-ratio zoom lenshaving the ability to focus at close range with only small aberrationfluctuations.

With reference to FIG. 1, a zoom lens 10 according to a first preferredembodiment of the present invention comprises, from object plane 12 toimage plane 14 along optical axis 16, a first lens group G1 having apositive refractive power, a second lens group G2 having negativerefractive power, a third lens group G3 having negative refractivepower, a fourth lens group G4 having positive refractive power, a fifthlens group G5 having positive refractive power, and a sixth lens groupG6 having negative refractive power. At least second lens group G2 movesimagewise and sixth lens group G6 moves objectwise such that, whenchanging the lens positional state from the extreme wide-angle state (W)to the extreme telephoto state (T), the axial distance (hereinafter,"air space") between first lens group G1 and second lens group G2increases, the air space between second lens group G2 and third lensgroup G3 increases, the air space between third lens group G3 and fourthlens group G4 decreases, the air space between fourth lens group G4 andfifth lens group G5 decreases, and the air space between fifth lensgroup G5 and sixth lens group G6 changes. Based on the aboveconfiguration, a zoom lens capable of increased variable power whilehaving a large aperture size can be achieved.

The aberration correction function for each lens group comprising thezoom lens according to a first preferred embodiment is now described.With continuing reference to FIG. 1, the divergence action isstrengthened by moving first lens group G1 and third lens group G3closer in the wide-angle state, and the off-axis light beam passingthrough first lens group G6 approaches the optical axis. As a result,the lens diameter of first lens group G1 is reduced and a sufficientback focus is ensured. In addition, by moving second lens group G2imagewise such that the air space between first lens group G1 and secondlens group G2 widens (increases) when changing the lens positional statefrom the wide-angle state to the telephoto state, the convergence actiondue to first lens group G1 in the telephoto state increases, and areduction in the overall length of the lens is realized. Also, bothsecond lens group G2 and third lens group G3 have negative refractivepower. This allows for the fluctuations in the off-axis aberrations tobe satisfactorily corrected since the height of the off-axis light beampassing therethrough changes.

In addition, fourth lens group G4 and fifth lens group G5 both have apositive refractive power. The fluctuation of off-axis aberrationsgenerated as the lens positional state changes can be satisfactorilycorrected by reducing (decreasing) the air space between fourth lensgroup G4 and fifth lens group G5 when changing the lens positional statefrom the wide-angle state to the telephoto state.

In the first preferred embodiment of the present invention, the off-axislight beam passing through second lens group G2 and fifth lens group G5is removed from the optical axis when the zoom lens is in the wide-anglestate. This allows for the fluctuation of coma generated as the fieldangle changes to be corrected. In particular, coma generated withrespect to the lower part light beam at second lens group G2 issatisfactorily corrected and coma generated with respect to the upperpart light beam at fifth lens group G5 is satisfactorily corrected.Also, the difference in height between the off-axis light beam and theon-axis light beam passing through second lens group G2 and fifth lensgroup G5 decreases as the lens positional state changes from thewide-angle state to the telephoto state, the fluctuation of off-axisaberrations generated as the lens positional state changes can becorrected. As a result, an increased zoom ratio can be achieved.

In the first preferred embodiment of the present invention, third lensgroup G3 and fourth lens group G4 principally correct on-axisaberrations. In other words, by independently correcting on-axisaberrations generated by third lens group G3 and fourth lens group G4,the fluctuation of on-axis aberrations generated as the lens positionalstate changes is corrected. As a result, an increased aperture size canbe achieved. Thus, the first preferred embodiment of the presentinvention is configured such that the signs of the refractive powers oflens groups G2 and G3 are the same, and the sign of the refractivepowers of lens groups G4 and G5 are the same. By clarifying theaberration correction function of each lens group, the coexistence of ahigh zoom ratio and a large aperture ratio is realized. Also, theoverall length of the zoom lens is reduced in the telephoto state byhaving the most imagewise sixth lens group G6 be of negative refractivepower. Negative distortion, which is easily generated in the wide-anglestate, is satisfactorily corrected by generating positive distortion inthe wide-angle state. In addition, in the first preferred embodiment ofthe present invention, it is preferable to provide an aperture stopbetween third lens group G3 and fifth lens group G5.

In light of the above design properties, several design conditions arepreferably satisfied to meet the above-identified objectives of thefirst preferred embodiment of the present invention. These designconditions are set forth immediately below. The first design conditionpertains to an appropriate value for the focal length of first lensgroup G1 to achieve the coexistence of a high zoom ratio and a largeaperture ratio. The first condition is expressed as

    1.0<f.sub.1 /(f.sub.w ·f.sub.t).sup.1/2 <1.6      (1)

wherein f₁ is the focal length of first lens group G1, f_(w) is thefocal length of the zoom lens in the wide-angle state, and f₁ is thefocal length of the zoom lens in the telephoto state. If f₁ /(f_(w)·f_(t))^(1/2) exceeds the upper limit of condition (1), it becomesdifficult to satisfactorily correct negative spherical aberrationgenerated independently by first lens group G1. Also, since the off-axislight beam impinging on first lens group G1 in the wide-angle statedeviates from the optical axis, an increase in the diameter of the lensbecomes unavoidable to ensure a sufficient amount of peripheral light.Conversely, if f₁ /(F_(w) ·f_(t))^(1/2) falls below the lower limit ofcondition (1), an increase in the overall lens length results, since theconvergence action due to first lens group G1 weakens.

To further reduce the overall lens length in the telephoto state, it ispreferable to set the upper limit of condition (1) to 1.45. In addition,to satisfactorily correct off-axis aberrations generated by first lensgroup G1 in the wide-angle state and to attain increased opticalperformance, it is preferable to set the lower limit of condition (1) to1.2.

The second design condition relates to attaining increased opticalperformance without inviting an increase in the lens diameter even inthe wide-angle state. In particular, condition (2) below stipulates theamount of movement of first lens group G1 as the lens positional statechanges from the wide-angle state to the telephoto state. Condition (2)is expressed as

    0.8<TL.sub.w /TL.sub.t <1.2                                (2)

wherein TL_(w) is the overall length of the lens in the wide-anglestate, and TL_(t) is the overall length of the lens in the telephotostate. If TL_(w) /TL_(t) exceeds the upper limit of condition (2), thecomposite refractive power from first lens group G1 to third lens groupG3 strengthens toward the negative, since the overall lens length in thewide-angle state is reduced. As a result, increased optical performancecan no longer be attained, since the off-axis light beam passing throughfirst lens group G1 to third lens group G3 approaches the optical axis,and fluctuations of coma with field angle increase. Conversely, ifTL_(w) /TL_(t) falls below the lower limit of condition (2), the overalllength of the lens in the wide-angle state increases. Consequently, theoff-axis light beam passing through first lens group G1 to third lensgroup G3 deviates excessively from the optical axis, which increases thelens diameter.

To achieve the coexistence of an increased zoom ratio and an increasedoptical performance in the zoom lens of the present invention, it ispreferred that the height of the off-axis light beam passing througheach lens group change greatly as the lens positional state changes. Inparticular, since the field angle is large in the wide-angle state, thecorrection of off-axis aberrations is vital. The off-axis aberrations inthe wide-angle state can be satisfactorily corrected by locating anaperture stop near the center of the zoom lens. Accordingly, asmentioned above, it is preferable to locate an aperture stop betweenthird lens group G3 and fourth lens group G4, or between fourth lensgroup G4 and fifth lens group G5. In particular, since there is a largeair space between third lens group G3 and fourth lens group G4 in thewide-angle state, it is preferable to locate an aperture stop betweenthird lens group G3 and fourth lens group G4 from the viewpoint ofreducing the lens diameter. Furthermore, it is optimal to locate theaperture stop near fourth lens group G4 to reduce the lens diameter ofeach lens group. When changing the lens positional state, the aperturestop may be moved either together with or independently of a moveablelens group. Since the air space between third lens group G3 and fourthlens group G4 narrows in the telephoto state, the lens barrelconstruction can be simplified by moving the aperture stop together withfourth lens group G4.

Accordingly, in the first preferred embodiment of the present invention,it is preferable, as mentioned above, to locate the aperture stopbetween third lens group G3 and fifth lens group G5, and to satisfy thefollowing design condition (3), which stipulates the on-axis spacebetween third lens group G3 and fourth lens group G4 in the wide-anglestate. Condition (3) is expressed as

    1.4<D.sub.34 /f.sub.w <2.0                                 (3)

wherein D₃₄ is the axial distance between third lens group G3 and fourthlens group G4 in the wide-angle state, and f_(w) is the focal length ofthe zoom lens in the wide-angle state. If D₃₄ /f_(w) exceeds the upperlimit of condition (3), the composite refractive power from first lensgroup G1 through third lens group G3 in the wide-angle state weakenstoward the negative. Also, the composite refractive power from fourthlens group G4 through sixth lens group G6 weakens toward the positive.In this case, the off-axis light beam passing through first lens groupG1 to third lens group G3 deviates from the optical axis. Thus, coma inthe peripheral part of the field is no longer satisfactorily corrected.Conversely, if D₃₄ /f_(w) falls below the lower limit in condition (3),the composite refractive power from first lens group G1 through thirdlens group G3 in the wide-angle state strengthens toward the negative.Also, the composite refractive power from fourth lens group G4 throughsixth lens group G6 strengthens toward the positive. In this case, therefractive power of each lens group strengthens. Thus, the fluctuationof on-axis aberrations generated as the lens positional state changescan no longer be satisfactorily corrected.

To further increase optical performance in the first preferredembodiment of the present invention, it is preferable to set the lowerlimit of condition (3) to 1.5, or to set the upper limit of condition(3) to 1.9.

It is also preferable for the first preferred embodiment of the presentinvention to satisfy a fourth design condition (4) to attain compactnessof the zoom lens and to increase optical performance and balance in thetelephoto state. Condition (4) stipulates the on-axis space betweenfirst lens group G1 and second lens group G2 in the telephoto state andis expressed as

    0.15<D.sub.12 /f.sub.t <0.40                               (4)

wherein D₁₂ is the axial distance between first lens group G1 and secondlens group G2 in the telephoto state, and f₅ is the focal length of thezoom lens in the telephoto state. If D₁₂ /f_(t) exceeds the upper limitof condition (4), the off-axis light beam passing through first lensgroup G1 in the telephoto state deviates excessively from the opticalaxis. Consequently, coma in the peripheral part of the field can nolonger be satisfactorily corrected. Conversely, if D₁₂ /f_(t) fallsbelow the lower limit in condition (4), the overall length of the lensin the telephoto state increases.

Further, in the first preferred embodiment of the present invention, itis also preferable to satisfy a fifth design condition to increaseoptical performance in the wide-angle state. Condition (5) stipulatesthe on-axis space between fourth lens group G4 and fifth lens group G5in the wide-angle state, and is expressed as

    0.4<D.sub.45 /f.sub.5 <0.7                                 (5)

wherein D₄₅ is the on-axis space between fourth lens group G4 and fifthlens group G5 in the wide-angle state, and f₅ is the focal length offifth lens group G5. If D₄₅ /f₅ exceeds the upper limit of condition(5), the off-axis light beam passing through fifth lens group G5 in thewide-angle state deviates excessively from the optical axis.Consequently, coma generated in the peripheral part of the field can nolonger be satisfactorily corrected. Conversely, if D₄₅ /f₅ falls belowthe lower limit in condition (5), the off-axis light beam passingthrough fifth lens group G5 in the wide-angle state excessivelyapproaches the optical axis. Consequently, the fluctuation of coma withfield angle can no longer be satisfactorily corrected.

It is also preferable in the first preferred embodiment of the presentinvention to introduce at least one aspherical surface in second lensgroup G2 to satisfactorily correct the fluctuation of coma due withfield angle in the wide-angle state, and to attain an even greaterdegree of optical performance. Generally, the aberration correctionfunction of an aspherical surface is broadly classified into two cases:the case wherein it is arranged near the aperture stop, it and the casewherein it is arranged at a position removed from the aperture stop. Inother words, if the aspherical surface is arranged near the aperturestop, it principally corrects on-axis aberrations. On the other hand, ifthe aspherical surface is arranged at a position removed from theaperture stop, it principally corrects off-axis aberrations.

If an aspherical surface is arranged in second lens group G2 throughwhich the off-axis light beam passing therethrough deviates from theoptical axis in the wide-angle state, it would result in the asphericalsurface being arranged near the aperture stop. Accordingly, in thiscase, the fluctuation of coma with field angle produced in thewide-angle state can be satisfactorily corrected. As a result, increasedoptical performance becomes possible.

In this case, it is preferable to satisfy a sixth design condition,expressed as

    1.5<f.sub.3 /f.sub.2 <2.5                                  (6)

wherein f₂ is the focal length of second lens group G2, and f₃ is thefocal length of third lens group G3. If f₃ /f₂ exceeds the upper limitof condition (6), the spherical aberration generated independently bysecond lens group G2 can no longer be satisfactorily corrected.Conversely, if f₃ /f₂ falls below the lower limit of condition (6), theoff-axis light beam passing through first lens group G1 deviates fromthe optical axis, since the composite principle point position of secondlens group G2 and third lens group G3 in the wide-angle state movesimagewise. As a result, the lens diameter increases.

To attain the coexistence of an increased aperture size and an increasedoptical performance in the telephoto state, it is vital to moresatisfactorily correct spherical aberration. Further, if the off-axislight beam in the wide-angle state passes through the zoom lens groupsfar removed from the optical axis, and the aperture ratio is made fixedwithout depending on a change in the lens positional state, then anincreased aperture size and an increased optical performance can be moreeffectively achieved. This is accomplished by introducing an asphericalsurface is introduced in lens group G5 through which the off-axis lightbeam passing therethrough widens in the telephoto state compared withthe wide-angle state.

Accordingly, it is preferable in the first preferred embodiment of thepresent invention to introduce at least one aspherical surface in fifthlens group G5. In this case, it is further preferable to satisfy aseventh design condition expressed as

    1.2<f.sub.4 /f.sub.5 <1.8                                  (7)

wherein f₄ is the focal length of fourth lens group G4, and f₅ is thefocal length of fifth lens group G5. If f₄ /f₅ exceeds the upper limitof condition (7), the overall length of the lens in the telephoto stateincreases. Conversely, if f₄ /f₅ falls below the lower limit ofcondition (7), the off-axis light beam passing through fifth lens groupG5 in the wide-angle state approaches the optical axis. Consequently,on-axis aberrations and off-axis aberrations can no longer be correctedindependently, and the predetermined optical performance can no longerbe achieved.

Furthermore, as discussed below, an aperture ratio on the order of FNO2.8 is realized in each Working Example of the present invention.Nevertheless, in the present invention, it is relatively easy, forexample, to reduce the zoom ratio and further increase the aperturesize, or to increase the FNO and further increase the zoom ratio. Inaddition, by axially moving at least one lens group when focusing, highoptical performance can be realized in each phototaking distance rangingfrom infinite focus to close-range focus.

A second preferred embodiment of the zoom lens of the present invention,comprises, objectwise to imagewise, a first lens group G1 havingpositive refractive power and arranged most objectwise, a second lensgroup G2 having negative refractive power and arranged imagewise of andadjacent first lens group G1, an intermediate lens group GM(corresponding to the six-group type fourth lens group G4) havingpositive refractive power and arranged imagewise of second lens groupG2, and a lens group GE (corresponding to the six-group type sixth lensgroup G6). In this case, when changing the lens positional state fromthe wide-angle state to the telephoto state, second lens group G2 movesimagewise and last lens group GE moves objectwise such that the airspace between first lens group G1 and second lens group G2 increases,and the air space between second lens group G2 and intermediate lensgroup GM decreases. Then, the abovementioned design conditions (1) and(2) are satisfied.

With reference now to FIG. 6, a third preferred embodiment of a zoomlens 35 of the present invention is described. Zoom lens 35 comprises,from object plane 12 to image plane 14 along optical axis 16, a firstlens group G1 having positive refractive power, a second lens group G2having negative refractive power, a third lens group G3 having negativerefractive power, a fourth lens group G4 having positive refractivepower and fifth lens group G5 having a positive refractive power. Whenchanging the lens positional state from the wide-angle state to thetelephoto state, at least second lens group G2 moves imagewise, and atleast one of first lens group G1 or fourth lens group G4 moves such thatthe air space between first lens group G1 and second lens group G2increases, the air space between second lens group G2 and third lensgroup G3 increases, the air space between third lens group G3 and fourthlens group G4 decreases, and the air space between fourth lens group G4and fifth lens group G5 decreases.

The aberration correction function of each lens group comprising zoomlens 35 according to the third preferred embodiment of the presentinvention is now described. With continued reference to FIG. 6, in thewide-angle state (W), first lens group G1 through third lens group G3are arranged close together. First lens group G1 through third lensgroup G3 have a strong negative composite refractive power, and fourthlens group G4 and fifth lens group G5 have a strong positive compositerefractive power. A sufficient back focus is obtained for thedistribution of refractive powers of zoom lens 35 as a reverse telephotosystem.

In the third preferred embodiment of the present invention, it isparticularly important to satisfactorily correct the fluctuation of comadue with field angle if covering a field angle that exceeds 70°. Byappropriately setting the lens group spacing such that the off-axislight beam passing through second lens group G2 to third lens group G3,and fifth lens group G5 in the wide-angle state deviates from theoptical axis, coma of the lower part light beam of second lens group G2to third lens group G3 is satisfactorily corrected. Also, coma of theupper part light beam of fifth lens group G5 is satisfactorilycorrected. In particular, it is preferable to appropriately set thefocal length of second lens group G2 and third lens group G3, asdescribed below. It is also preferable to arrange first lens group G1and second lens group G2 such that they are close together, and toensure that the off-axis light beam passing through first lens group G1does not excessively deviate from the optical axis.

By moving at least second lens group G2 imagewise such that the airspace between first lens group G1 and second lens group G2 widens(increases) when changing the lens positional state from the wide-anglestate to telephoto state, the convergence action due to first lens groupG1 in the telephoto state strengthens and the overall length of the lensdecreases. In addition, by moving second lens group G2 and third lensgroup G3 imagewise and narrowing the air space between third lens groupG3 and the aperture stop (discussed below) such that the air spacebetween second lens group G2 and third lens group G3 widens (increases)when changing the lens positional state from the wide-angle state to thetelephoto state, the lateral magnification of second lens group G2 andthird lens group G3 increases, and an increased zoom ratio is achieved.In addition, the off-axis light beam passing through second lens groupG2 and third lens group G3 approaches the optical axis. Thus, thefluctuation of off-axis aberrations as the lens positional state changescan be satisfactorily corrected.

By narrowing (decreasing) the air space between fourth lens group G4 andfifth lens group G5 when changing the lens positional state from thewide-angle state to the telephoto state, the off-axis light beam passingthrough fifth lens group G5 and removed from the optical axis in thewide-angle state approaches the optical axis as the telephoto state isapproached. Thus, the fluctuation of off-axis aberrations generated whenthe lens positional state changes can be satisfactorily corrected.

To realize an increased aperture size, it is important to satisfactorilycorrect on-axis aberrations generated by each lens group. In the zoomlens of the third preferred embodiment of the present invention, thirdlens group G3 and fourth lens group G4 contribute principally to on-axisaberrations. Since third lens group G3 and fourth lens group G4 arepositioned near the center of the zoom lens (see FIG. 6), and arearranged relatively near to the aperture stop (discussed below), theoff-axis light beam tends to pass through these lens groups near theoptical axis. This reduces off-axis aberrations. By satisfactorilycorrecting the on-axis aberrations generated by third lens group G3 andfourth lens group G4, the fluctuation of on-axis aberrations generatedas the lens positional state changes can be satisfactorily corrected.This allows for an increased aperture size to be achieved. Also, byclarifying the aberration correction function of each lens group andsatisfactorily correcting the aberrations generated by each lens groupin the third preferred embodiment of the present invention as describedabove, the coexistence of an increased zoom ratio and an increasedaperture size (i.e., aperture ratio) is realized.

In the third preferred embodiment of the present invention, it ispreferable to satisfy design condition (8), which stipulates theappropriate range for the radius of curvature of the lens surfacescomprising second lens group G2. Condition (8) is expressed as

    0.1<(Ave. C)·f.sub.w <0.6                         (8)

wherein "Ave. C" is the average value of the absolute value of theparaxial curvature of each lens surface comprising second lens group G2,and f_(w) is the focal length of the zoom lens in the wide-angle state.

If (Ave. C)·f_(w) exceeds the upper limit of condition (8), it isdifficult to correct the off-axis aberrations in the wide-angle state,since the absolute value of the radius of curvature increases.Conversely, if (Ave. C)·f_(w) falls below the lower limit of condition(8), a sufficient back focus in the wide-angle state cannot be obtained.In addition, it is further preferable in the present invention to setthe upper limit of condition (8) to 0.5 to obtain higher opticalperformance.

It is also preferable that the zoom lens of the third preferredembodiment of the present invention satisfy design condition (9)relating to maintaining lens compactness. Condition (9) is expressed as

    0.45<D.sub.2 /f.sub.1 <0.55                                (9)

wherein D₂ is the axial distance between first lens group G1 and secondlens group G2 in the wide-angle state, and f₁ is the focal length offirst lens group G1.

If D₂ /f₁ exceeds the upper limit of condition (9), the lens diameter offirst lens group G1 increases, since the off-axis light beam passingthrough first lens group G1 in the telephoto state deviates excessivelyfrom the optical axis. Conversely, if D₂ /f₁ falls below the lower limitin condition (9), the overall length of the lens in the telephoto stateincreases.

In addition, for satisfactorily correcting coma generated in thewide-angle state, it is preferable that lens group G2 of the zoom lenscomprise, objectwise to imagewise, a negative lens L21 having animagewise concave surface, and a cemented lens L22 comprising abiconcave lens L22a and a positive lens L22b (see e.g., zoom lens 40 ofFIG. 7). It is further preferable that negative lens L21 have a meniscusshape to attain higher performance. Also, it is preferable that anaperture stop AS be arranged adjacent fourth lens group G4 (see, e.g.,zoom lens 40 of FIG. 7).

The location of the aperture stop necessary to attain increased variablemagnification and an increased optical performance is now described.Generally, the off-axis light beam passing through the lens groupsremoved from the aperture stop tends to be removed from the opticalaxis. Since it is easy to independently correct on-axis aberrations andoff-axis aberrations in lens groups through which the off-axis lightbeam passing therethrough deviates from the on-axis light beam, lensgroups removed from the aperture stop are suited to the correction ofoff-axis aberrations. To satisfactorily correct off-axis aberrationsgenerated as the lens positional state changes, it is preferred thatthere be many lens groups wherein the height of the off-axis light beampassing therethrough changes greatly as the lens positional statechanges.

Accordingly, in the zoom lens of the third preferred embodiment of thepresent invention, the aperture stop is located near the center of thezoom lens. Each lens group in the zoom lens is moved as the lenspositional state changes such that the air space adjacent to theaperture stop changes greatly. Consequently, the off-axis aberrationsgenerated as the lens positional state changes are satisfactorilycorrected, and an increased zoom ratio and an increased opticalperformance is achieved. To attain increased optical performance inparticular, it is preferable to arrange the aperture stop adjacentfourth lens group G4.

More particularly, it is preferable to locate the aperture stop betweenthird lens group G3 and fourth lens group G4 to attain a reduction inthe lens diameter simultaneous with attaining increased opticalperformance. If the aperture stop is arranged between third lens groupG3 and fourth lens group G4, it is preferable that third lens group G3include a negative lens having an objectwise concave surface, and thatthe zoom lens satisfy the design condition

    0.7<|r.sub.a |/D.sub.a <1.3              (10)

wherein r_(a) is the radius of curvature of the objectwise lens surfaceof the negative lens (e.g., lens L3a in FIG. 9), and Da is the axialseparation between the aperture stop and the objectwise lens surface ofthe negative lens in the wide-angle state. Condition (10) is necessaryfor more satisfactorily correction on-axis aberrations in the telephotostate.

If |r_(a) |/D_(a) exceeds the upper limit of condition (10), sufficientback focus cannot be ensured in the wide-angle state. Conversely, if|r_(a) |/D_(a) falls below the lower limit of condition (10), sphericalaberration generated in the telephoto state cannot be satisfactorilycorrected, and an increased optical performance cannot be attained.Off-axis aberrations in the wide-angle state can be more satisfactorilycorrected by setting the lower limit to 0.85. Also, even higher opticalperformance in the telephoto state can be obtained by setting the upperlimit to 1.2.

In addition, in the zoom lens of the third preferred embodiment of thepresent invention, it is preferable that fifth lens group G5 includefirst and second subgroups, and that the zoom lens satisfy the designcondition

    0.15<D.sub.5 /f.sub.w <0.45                                (11)

wherein f_(w) is the focal length of the zoom lens in the wide-anglestate, and D₅ is the air space between the first and second subgroups ofthe lens group G5. Condition (11) is necessary for satisfactorilycorrecting coma generated with respect to the upper part light beam inthe wide-angle state. In the present invention, it is important tosatisfactorily correct off-axis aberrations generated by each lens groupto attain an increased aperture size. In particular, the off-axis lightbeam in the wide-angle state deviates from the optical axis and theon-axis light beam in the telephoto state widens and passes throughfifth lens group G5. Thus, it is preferable to divide fifth lens groupG5 into first and second positive subgroups, where the first subgroupprincipally corrects on-axis aberrations, while the second subgroupprincipally corrects off-axis aberrations.

If D₅ /f_(w) exceeds the upper limit of condition (11), the lensdiameter increases, since the off-axis light beam passing through thesecond subgroup in the wide-angle state deviates excessively from theoptical axis. In zoom lenses of SLR cameras in particular, since thediameter of the mount (i.e., flange) that attaches the lens barrel tothe camera body is of a predetermined size, increasing the lens diameterof the second subgroup presents a serious problem. Conversely, if D₅/f_(w) falls below the lower limit of condition (11), coma generatedwith respect to the upper part light beam in the wide-angle state can nolonger be satisfactorily corrected.

In addition, in the zoom lens of the third preferred embodiment of thepresent invention, it is preferable to use one or more asphericalsurfaces in fifth lens group G5 to attain higher performance. Further,it is preferable to use an aspherical surface in the first subgroup oflens group G5, which principally corrects on-axis aberrations.

A fourth preferred embodiment of the zoom lens of the present inventionis now described. This fourth preferred embodiment has the same lensgroup configuration of the third preferred embodiment (see FIG. 6), andpreferably satisfies the design conditions set forth below. First, it ispreferable that the zoom lens of the fourth preferred embodiment of thepresent invention satisfy the design condition

    0.4<f.sub.1 /f.sub.t <0.7                                  (12)

wherein f_(t) is the focal length of the zoom lens in the telephotostate, and f₁ is the focal length of first lens group G1 in thetelephoto state. Design condition (12) stipulates an appropriate rangefor the focal length of first lens group G1, and is a necessarycondition for reducing the overall length of the lens in the telephotostate. If f₁ /f_(t) exceeds the upper limit of condition (12), theoverall length of the lens in the telephoto state increases. Conversely,if f₁ /f_(t) falls below the lower limit of condition (12), the off-axislight beam passing through first lens group G1 in the wide-angle statedeviates from the optical axis, generating excessive coma. Thus, thepredetermined optical performance cannot be obtained.

It is also preferable that in the zoom lens of the third and fourthpreferred embodiments of the present invention satisfy at least one ofthe design conditions

    1.2<f.sub.3 /f.sub.2 <2.2                                  (13)

    0.7<f.sub.4 /f.sub.5 <1.5                                  (14)

wherein f₂ is the focal length of second lens group G2, f₃ is the focallength of third lens group G3, f₄ is the focal length of fourth lensgroup G4, and f₅ is the focal length of fifth lens group G5,respectively. Design conditions (13) and (14) are necessary for furtherincreasing optical performance while maintaining the predetermined zoomratio. If f₃ /f₂ exceeds the upper limit of condition (13), the off-axisaberrations generated by second lens group G2 in the wide-angle statecan no longer be satisfactorily corrected. Conversely, if f₃ /f₂ fallsbelow the lower limit of condition (13), spherical aberration generatedby third lens group G3 in the telephoto state can no longer besatisfactorily corrected. If f₄ /f₅ exceeds the upper limit in condition(14), the off-axis aberrations cannot be satisfactorily corrected, sincethe off-axis light beam passing through fifth lens group G5 in thewide-angle state approaches the optical axis. Conversely, if f₄ /f₅falls below the lower limit, the negative spherical aberration generatedby fourth lens group G4 in the telephoto state can no longer besatisfactorily corrected.

A fifth preferred embodiment of the zoom lens of the present inventioncapable of close-range focus is now described. With reference to FIG.10, zoom lens 55 comprises from object plane 12 to image plane 14 alongoptical axis 16, at least a first lens group G1 having a positiverefractive power, a second lens group G2 having a negative refractivepower, a third lens group G3 having a negative refractive power, and afourth lens group G4 having a positive refractive power. Accordingly,second lens group G2 is moved imagewise and at least one lens group offirst lens group G1 and fourth lens group G4 moves such that, whenchanging the lens positional state from the wide-angle state to thetelephoto state, the air space between first lens group G1 and secondlens group G2 increases, the air space between second lens group G2 andthird lens group G3 increases, and the air space between third lensgroup G3 and fourth lens group G4 decreases. The close-range focus(i.e., focus from an infinite object to a close-range object) isachieved by moving third lens group G3 axially objectwise along opticalaxis 16, as shown in FIG. 10. In this manner, a zoom lens is achievedthat can easily control the lens position of the focusing group whileensuring a high variable power ratio and a large aperture ratio by thefollowing steps: (i) appropriately setting the composite focal length offirst lens group G1 and second lens group G2, and (ii) appropriatelysetting the focal length of third lens group G3.

The design conditions for reducing the amount of focusing movement ofthird lens group G3 are now discussed. With continuing reference to FIG.10, when the position of object plane 12 with respect to third lensgroup G3 moves axially a small amount δ, it is necessary to move axiallythird lens group G3 by a corresponding amount Δ to make the position ofobject plane 12 fixed with respect to fourth lens group G4. In thiscase, the amount of focusing movement Δ of third lens group G3 is givenby the mathematical expression

    Δ={β.sub.3.sup.2 /(β.sub.3.sup.2 -1)}·δ(a)

wherein β₃ is the lateral magnification of third lens group G3.

If β₃ ² /(β₃ ² -1) in expression (a) is defined as "k", then k dependson the value of β₃ ², and the conditions set forth in expressions (b)and (c):

    1≦k(β.sub.3.sup.2 >1)                          (b)

    0>k(β.sub.3.sup.2 <1)                                 (c)

Accordingly, if β₃ ² >1, it is necessary that k approach 1 as much aspossible, i.e., that 1/β₃ approaches 0, to reduce the size of focusingmovement amount Δ. In addition, if β₃ ² <1, it is necessary that kapproach 0 as much as possible, i.e., that β₃ approaches 0.

Thus, the focusing movement of third lens group G3 is reduced by makingthe lateral magnification β₃ of third lens group G3 approach 0. Makingβ₃ approach 0 means that the composite refractive power of first lensgroup G1 and second lens group G2 weakens in the extreme. Accordingly,it is preferable to appropriately set the composite focal length offirst lens group G1 and second lens group G2, and it is vital to satisfystep (i), above.

In addition, if the refractive power of third lens group G3 is stronglynegative, the focusing movement amount becomes small since the lateralmagnification β₃ of third lens group G3 approaches 0. Nevertheless, ifthe negative refractive power of third lens group G3 strengthens, therefractive power of each lens comprising third lens group G3strengthens. Consequently, aberrations arise. Accordingly, it ispreferable to appropriately set the refractive power of third lens groupG3, and it is vital to satisfy step (ii), above.

Generally, in the optimal solution of a zoom lens, it is necessary notonly to simply satisfy a predetermined optical performance, but also tosimultaneously achieve a reduction in the size and weight of the zoomlens. To this end, it is preferred that the fifth preferred embodimentof the zoom lens of the present invention satisfy design conditions (15)and (16), expressed as

    -0.5<φ12.sub.t ·f.sub.t <0.3                  (15)

    0.8<|f.sub.3 |/(f.sub.w ·f.sub.t).sup.1/2 <1.2(16)

wherein φ12_(t) is the composite refractive power of first lens group G1and second lens group G2 in the telephoto state.

Design condition (15) stipulates the composite refractive power of firstlens group G1 and second lens group G2 in the telephoto state, anddesign condition (16) stipulates the focal length of third lens groupG3. As discussed above, it is preferable to appropriately set thecomposite focal length of first lens group G1 and second lens group G2to reduce the focusing movement amount of third lens group G3.

If φ12_(t) ·f_(t) exceeds the upper limit of condition (15), theoff-axis light beam passing through first lens group G1 in the telephotostate deviates excessively from the optical axis. This makes itnecessary to increase the size of the lens diameter to ensure asufficient quantity of light in the peripheral part of the field. Ifφ12_(t) ·f_(t) falls below the lower limit, the overall lens length inthe telephoto state increases. To further reduce the focusing movementof third lens group G3 in the telephoto state, and to further increasethe speed of the autofocus operation, it is preferable to either set thelower limit of condition (15) to -0.4 or to set the upper limit to 0.15.If |f₃ |/(f_(w) ·f_(t))^(1/2) exceeds the upper limit of condition (16),the focusing movement amount increases when focusing at close range,since the focal length of third lens group G3 increases. As a result,the speed of the focusing operation cannot be increased and thecompactness of the lens system can not be attained. To do so, it wouldbe necessary to unacceptably widen the air space between third lensgroup G3 and the lens group arranged adjacent and objectwise orimagewise thereof. Conversely, if |f₃ |/(f_(w) ·f_(t))^(1/2) falls belowthe lower limit of condition (16), the fluctuation of variousaberrations generated when focusing at close range increases, since thefocal length of third lens group G3 decreases. As a result, thepredetermined optical performance can no longer be maintained in eachphototaking distance state from the infinite-focus state to theclose-range focus state. Accordingly, in the fifth preferred embodimentof the present invention, a fifth lens group G5 having a positiverefractive power is provided imagewise of fourth lens group G4. Also, itis preferable, when changing the lens positional state from thewide-angle state to the telephoto state, that fifth lens group G5 moveobjectwise such that the air space between fourth lens group G4 andfifth lens group G5 decreases.

In a sixth preferred embodiment of the present invention, a sixth lensgroup G6 having a negative refractive power is provided imagewise offifth lens group G5 in the above-described fifth embodiment. Further, itis preferable, when changing the lens positional state from thewide-angle state to the telephoto state, that sixth lens group G6 moveobjectwise such that the air space between fourth lens group G4 andsixth lens group G6 changes.

The sixth preferred embodiment of the zoom lens of the present inventionallows for the realization of a zoom lens having an aperture ratio onthe order of FNO 2.8 and a zoom ratio exceeding 5×. With reference toFIG. 10, zoom lens 55 according to the sixth preferred embodiment of thepresent invention comprises, from object plane 12 to image plane 14along optical axis 16, a first lens group G1 having a positiverefractive power, a second lens group G2 having a negative refractivepower, a third lens group G3 having a negative refractive power, afourth lens group G4 having a positive refractive power, a fifth lensgroup G5 having a positive refractive power, and a sixth lens group G6having a negative refractive power. It is preferable to move second lensgroup G2 imagewise and to move sixth lens group G6 objectwise such that,when changing the lens positional state from the wide-angle state to thetelephoto state, the air space between first lens group G1 and secondlens group G2 increases, the air space between second lens group G2 andthird lens group G3 increases, the air space between third lens group G3and fourth lens group G4 decreases, the air space between fourth lensgroup G4 and fifth lens group G5 decreases, and the air space betweenfifth lens group G5 and sixth lens group G6 changes.

The function of each lens group in the abovementioned six-group typezoom lens according to this sixth preferred embodiment is now described.In the fifth and sixth preferred embodiments of the present invention,the divergence action is strengthened by moving first lens group G1 andthird lens group G3 closer to one another in the wide-angle state. As aresult, the off-axis light beam passing through first lens group G1approaches the optical axis. Thus, the lens diameter of first lens groupG1 is reduced and a sufficient back focus is ensured. In addition, bymoving second lens group G2 imagewise such that the air space betweenfirst lens group G1 and second lens group G2 widens when changing thelens positional state from the wide-angle state to the telephoto state,the convergence action due to first lens group G1 in the telephoto stateincreases, and a reduction in the overall length of the lens isrealized. Furthermore, both second lens group G2 and third lens group G3have negative refractive power, and the fluctuation of off-axisaberrations can be satisfactorily corrected. This is due to the wideningof the air space between second lens group G2 and third lens group G3when changing the lens positional state from the wide-angle state to thetelephoto state, which causes the height of the off-axis light beampassing therethrough to change. Fourth lens group G4 and fifth lensgroup G5 also both have positive refractive power. Thus, the fluctuationof off-axis aberrations generated as the lens positional state changescan be satisfactorily corrected by reducing the air space between fourthlens group G4 and fifth lens group G5 when changing the lens positionalstate from the wide-angle state to the telephoto state.

Also, in the fifth and sixth preferred embodiments of the zoom lens ofthe present invention, the fluctuation of coma with field angle can besatisfactorily corrected, since the off-axis light beam passing throughsecond lens group G2 and fifth lens group G5 removed from the opticalaxis when the lens is in the wide-angle state. In particular, comagenerated with respect to the lower part light beam at second lens groupG2 is satisfactorily corrected and coma generated with respect to theupper part light beam at fifth lens group G5 is satisfactorilycorrected.

Also, the difference in the height between the off-axis light beam andthe on-axis light beam passing through second lens group G2 and fifthlens group G5 decreases as the lens positional state changes from thewide-angle state to the telephoto state. Thus, the fluctuation ofoff-axis aberrations generated as the lens positional state changes canbe satisfactorily corrected. As a result, an increased zoom ratio can beachieved. Furthermore, third lens group G3 and fourth lens group G4principally correct on-axis aberrations. In other words, by thesatisfactory correcting on-axis aberrations generated by third lensgroup G3 and fourth lens group G4, the fluctuation of on-axisaberrations generated as the lens positional state changes is corrected.As a result, an increased aperture size can be achieved.

The fifth and sixth preferred embodiments of the present invention areconstituted such that the signs of the refractive powers of second lensgroup G2 and third lens group G3 are the same, and the sign of therefractive powers of fourth lens group G4 and fifth lens group G5 arethe same. Thus, by clarifying the aberration correction function of eachlens group, the coexistence of an increased zoom ratio and an increasedaperture size is realized.

In the sixth preferred embodiment of the present invention, the overalllength of the zoom lens is reduced in the telephoto state by makingsixth lens group G6 having a negative refractive power the mostimagewise lens group of the zoom lens. In addition, negative distortion,which is easily generated in the wide-angle state, is satisfactorilycorrected by generating positive distortion in the wide-angle state.

Also, in the fifth and sixth preferred embodiments of the presentinvention, it is preferred that the zoom lens satisfy the designcondition

    2<|φMAX|·f.sub.t <8         (17)

wherein φMAX is the refractive power of the lens group having thestrongest refractive power among the plurality of lens groups. Condition(17) stipulates the refractive power of the lens group having thestrongest refractive power among the plurality of lens groups. Toachieve increased optical performance while ensuring a large apertureratio, it is vital to satisfactorily correct on-axis aberrationsgenerated by each lens group. Also, it is important to appropriatelyweaken the refractive power of each lens group.

If |φMAX|·f_(t) exceeds the upper limit of condition (17), on-axisaberrations generated by each lens group cannot be satisfactorilycorrected. Also, the fluctuation of various aberrations generated as thelens positional state changes can no longer be satisfactorily corrected.Conversely, if |φMAX|·f_(t) falls below the lower limit of condition(17), it is necessary to greatly change the air spaces between lensgroups to obtain the predetermined zoom ratio. As a result, the off-axislight beam passing through the lens groups removed from the aperturestop deviates from the optical axis, thereby increasing the lensdiameter.

Also, in the fifth and sixth preferred embodiments of the presentinvention, it is preferable to satisfy the design condition

    0.9<|φ2+φ3|·f.sub.w <1.3(18)

wherein φ2 is the refractive power of second lens group G2 and φ3 isrefractive power of third lens group G3. Condition (18) stipulates thecomposite refractive power of second lens group G2 and third lens groupG3 in the wide-angle state. If the axial separation between theprinciple points between the second lens group G2 and third lens groupG3 is given as d, then the composite refractive power of second lensgroup G2 and third lens group G3 can be expressed as φ2+φ3-dφ2φ3.However, since second lens group G2 and third lens group G3 are closetogether in the wide-angle state, the principle point space is small, sothat the effect of the term dφ2φ3 is negligible. Consequently, incondition (18), the sum of the refractive powers of second lens group G2and third lens group G3 effectively serves to stipulate the compositerefractive power of second lens group G2 and third lens group G3.

If |φ2+φ3|·f_(w) exceeds the upper limit of condition (18), the off-axislight beam passing through second lens group G2 and third lens group G3in the wide-angle state approaches the optical axis too closely, and thefluctuation of coma with field angle can no longer be satisfactorilycorrected. Conversely, if |φ2+φ3|·f_(w) falls below the lower limit ofcondition (18), the off-axis light beam passing through first lens groupG1 in the wide-angle state deviates too greatly from the optical axis,and excessive coma is generated in the peripheral part of the imageplane.

To attain the coexistence of a high zoom ratio and an increased aperturesize, it is necessary that the height of the off-axis light beam passingthrough each lens group change greatly as the lens positional statechanges, as discussed above. Generally, if the aperture stop is locatednear the center of the zoom lens, the fluctuation of off-axisaberrations generated as the lens positional state changes can besatisfactorily corrected. Accordingly, in the fifth and sixth preferredembodiments of the present invention, it is preferable to locate theaperture stop between third lens group G3 and fourth lens group G4.

In addition, in the fifth and sixth preferred embodiments of the presentinvention, it is preferable to satisfy the following design condition(19):

    0.7<|f.sub.3 |/f.sub.4 <1.0.             (19)

Design condition (19) stipulates the ratio of the focal length of thirdlens group G3 to the focal length of fourth lens group G4. If |f₃ |/f₄exceeds the upper limit of condition (19), coma with respect to theupper part light beam in the wide-angle state can no longer besatisfactorily corrected. Conversely, if |f₃ |/f₄ falls be below thelower limit of condition (19), coma with respect to the lower part lightbeam in the wide-angle state can no longer be satisfactorily corrected.

In addition, in the fifth and sixth preferred embodiments of the presentinvention, it is preferred that the zoom lens satisfy the designcondition

    1.5<f.sub.1 /D.sub.12t <2.5                                (20)

wherein D_(12t) is the axial distance between first lens group G1 andsecond lens group G2 in the telephoto state. Design condition (20) isfor the purpose of attaining compactness of the lens system in thetelephoto state. If f₁ /D_(12t) exceeds the upper limit of condition(20), the convergence action of first lens group G1 weakens.Consequently, the overall length of the lens can no longer besufficiently shortened. Conversely, if f₁ /D_(12t) falls be below thelower limit of condition (20), the off-axis light beam passing throughfirst lens group G1 deviates from the optical axis. Consequently, acompact lens diameter can no longer be attained.

With reference now to FIG. 15, a zoom lens according to a seventhpreferred embodiment of the present invention is now described. Zoomlens 80 comprises, from object plane 12 to image plane 14 along opticalaxis 16, a first lens group G1 having positive refractive power, asecond lens group G2 having negative refractive power, a third lensgroup G3 having negative refractive power, a fourth lens group G4 havingpositive refractive power, a fifth lens group G5 having positiverefractive power, and a sixth lens group G6 having positive refractivepower. At least second lens group G2 moves imagewise and fifth lensgroup G5 moves objectwise such that, when changing the lens positionalstate from the wide-angle state to the telephoto state, the air spacebetween the first lens group and second lens group increases, the airspace between the second lens group and third lens group increases, theair space between the third lens group and fourth lens group decreases,the air space between the fourth lens group and fifth lens group and thespace between the fifth lens group and sixth lens group change,respectively. An aperture stop (not shown) is arranged between firstlens group G1 and sixth lens group G6. Based on this configuration, thecoexistence of an increased zoom ratio and an increased aperture size isachieved.

To realize an increased zoom ratio, it is necessary to respectivelycorrect the fluctuation of on-axis aberrations and off-axis aberrationsgenerated as the lens positional state changes. Fluctuation in on-axisaberrations can be controlled by satisfactorily correcting on-axisaberrations generated by each lens group. However, the location of anaperture stop to achieve such correction is vital. Generally, lensgroups removed from the aperture stop are suited to the correction ofoff-axis aberrations, since the off-axis light beam passing therethroughis off-axis. Fluctuations of off-axis aberrations generated as the lenspositional state changes can be satisfactorily corrected when the heightof the off-axis light beam passing through each lens group changesgreatly with the lens positional state. By arranging the aperture stopat or near the center of the zoom lens, and designing the zoomtrajectory of the plurality of lenses such that the air spacesurrounding the aperture stop changes greatly when changing the lenspositional state, the fluctuation of off-axis aberrations generated asthe lens positional state changes can be satisfactorily corrected, asmentioned above. Thus, in the seventh preferred embodiment of thepresent invention, the coexistence of an increased zoom ratio and anincreased optical performance can be attained, since the aperture stopis arranged imagewise of first lens group G1 and objectwise of sixthlens group G6.

The aberration correction function of each lens group comprising thezoom lens according to the seventh preferred embodiment of the presentinvention is now described. In the wide-angle state, first lens group G1to third lens group G3 are close together and have a strong negativecomposite refractive power. The arrangement of refractive powers of theentire lens system is that of a reverse telephoto system. As such, asufficient back focus is obtained by widening the space between thethird lens group and the fourth lens group. In particular, if the fieldangle in the extreme wide-angle state exceeds 70°, it is important tosatisfactorily correct the fluctuation of coma with field angle. This isachieved by appropriately setting the lens group spacing such that theoff-axis light beam passing through second lens group G2 and third lensgroup G3 as well as fifth lens group G5 and sixth lens group G6 deviatesfrom the optical axis in the wide-angle state. This allows for thecorrection of coma with respect to the lower part light beam at secondlens group G2 and third lens group is satisfactorily corrected. Alsocoma with respect to the upper part light beam at fifth lens group G5and sixth lens group is satisfactorily corrected. It is also preferableto appropriately set the focal length of second lens group G2 and thirdlens group, to arrange first lens group G1 and second lens group suchthat they are close together, and to ensure that the off-axis light beampassing through first lens group G1 does not excessively deviate fromthe optical axis. Also, by moving at least second lens group G2imagewise such that the air space between first lens group G1 and secondlens group G2 widens when changing the lens positional state from thewide-angle state to the telephoto state, the convergence action due tofirst lens group G1 in the telephoto state strengthens. This decreasesthe overall lens length.

Further, lens group G2 and third lens group G3 move imagewise, and theair space between third lens group G3 and the aperture stop narrows suchthat the air space between second lens group G2 and third lens groupwidens when changing the lens positional state from the wide-angle stateto the telephoto state. Consequently, an increased zoom ratio can berealized, since the size of the lateral magnification of second lensgroup G2 and third lens group G3 increases. In addition, thefluctuations of off-axis aberrations as the lens positional statechanges can be satisfactorily corrected, since the off-axis light beampassing through second lens group G2 and third lens group G3 graduallyapproaches the optical axis. Also, by narrowing the air space betweenfourth lens group G4 and fifth lens group G5 when changing the lenspositional state from the wide-angle state to the telephoto state, theoff-axis light beam passing through fifth lens group G5 in thewide-angle state deviates from the optical axis, and the off-axis lightbeam approaches optical axis as the telephoto state is approached. Thisallows for the fluctuation of off-axis aberrations generated when thelens positional state changes to be satisfactorily corrected.

Generally, for interchangeable lenses ideally suited to single lensreflex cameras and the like, the coupling flange between the camera bodyand the lens barrel is constrained in the radial direction. Accordingly,the off-axis light beam passing through the lens groups arrangedimagewise of the aperture stop is close to the on-axis light beam.Consequently, it is difficult to satisfactorily correct coma withrespect to the upper part light beam, generated as the lens positionalstate changes. Thus, it is preferable to locate fourth lens group G4,fifth lens group G5 and sixth lens group G6, each having positiverefractive powers, imagewise of the aperture stop. When changing thelens positional state from the wide-angle state to the telephoto state,coma with respect to the upper part light beam can be corrected bynarrowing the air space between fourth lens group G4 and fifth lensgroup G5 and by changing the height of the off-axis light beam passingthrough fifth lens group G5. Also, the fluctuation of coma with respectto the upper part light beam generated in the intermediate focal lengthstate can be satisfactorily corrected by changing the air space betweenfifth lens group G5 and sixth lens group G6.

The seventh preferred embodiment of the present invention preferablysatisfies several design conditions. Design condition (21) stipulatesthe focal length of fifth lens group G5 and sixth lens group G6 and isexpressed as

    0.5<f.sub.5 /f.sub.6 <2.0                                  (21)

wherein f₅ and f₆ are the focal lengths of lens group G5 and G6,respectively.

If f₅ /f₆ exceeds the upper limit of condition (21), the off-axis lightbeam in the wide-angle state passes through sixth lens group G6 removedfrom the optical axis. Thus, the light beam is vignetted by the couplingflange that couples the lens to the camera body, and the amount of lightat the peripheral part of the image plan is reduced. Conversely, if f₅/f₆ falls below the lower limit of condition (21), the fluctuations ofoff-axis aberrations generated as the lens positional state changes canno longer be satisfactorily corrected.

Design condition (22) stipulates the quantity of movement of first lensgroup G1 when changing the lens positional state, and is expressed as

    -0.2<D.sub.1 /(F.sub.t -f.sub.w)<0.30                      (22)

wherein D₁ is the amount of axial movement of lens group G1 when zoomingfrom the maximum wide-angle state to the maximum telephoto state.

If D₁ /(f_(t) -f_(w)) exceeds the upper limit of condition (22), thepositive composite refractive power from first lens group G1 to thirdlens group G3 in the wide-angle state strengths toward the negative.Also, the composite refractive power from fourth lens group G4 to sixthlens group G6 strengthens toward the positive. Further, the asymmetry ofthe distribution of refractive powers of the entire lens system becomesmore pronounced. As a result, negative distortion in the wide-anglestate can not be corrected. Conversely, if D₁ /(f_(t) -f_(w)) fallsbelow the lower limit of condition (22), the overall length of the lensin the telephoto state shortens, and the off-axis light beam passingthrough the first lens group deviates from the optical axis.

As a result, the lens diameter of first lens group G1 increases. In thezoom lens of the seventh preferred embodiment of the present invention,it is preferable to locate the aperture stop between third lens group G3and fourth lens group G4 to obtain a higher optical performance in anarbitrary lens positional state. In particular, it is preferable to movethe aperture stop together with the fourth lens group when changing thelens positional state.

In the seventh preferred embodiment of the zoom lens of the presentinvention, it is preferable to satisfy at least one of the designconditions, expressed as

    0.4<|D.sub.2 |/(f.sub.w ·f.sub.t).sup.1/2 <0.7(D.sub.2 <0)                                          (23)

    0.4<D.sub.5 /(f.sub.w ·f.sub.t).sup.1/2 <0.8      (24)

to achieve a satisfactory optical performance in any arbitrary lensposition state. In design conditions (23) and (24), D₂ is the amount ofaxial movement of second lens group G2 when changing the lens positionalstate from the wide-angle state to the telephoto state, and D₅ is theamount of axial movement of fifth lens group G5 when changing the lenspositional state from the wide-angle state to the telephoto state. Here,an objectwise movement is positive. Design condition (23) stipulates theamount of movement of second lens group G2 as the lens positional statechanges.

If |D₂ |/(f_(w) ·f_(t))^(1/2) exceeds the upper limit of condition (23),the amount of movement of first lens group G1 increases when the lenspositional state changes from the wide-angle state to the telephotostate (since the amount of movement of second lens group G2 decreases).The zoom lens barrel of the zoom lens moves each lens group inaccordance with a predetermined movement ratio. However, since the lensdiameter of first lens group G1 is large, the lens barrel constructionbecomes complex if the amount of movement for lens group G1 increases.Accordingly, If |D₂ |/(f_(w) ·f_(t))^(1/2) exceeds the upper limit ofcondition (23), the lens barrel construction becomes complex.Conversely, if |D₂ |/(f_(w) ·f_(t))^(1/2) falls below the lower limit ofcondition (23), the size of the lens diameter increases, since theoff-axis light beam passing through first lens group G1 and second lensgroup G2 in the wide-angle state deviates excessively from the opticalaxis.

Design condition (24) stipulates the amount of movement of fifth lensgroup G5 as the lens positional state changes. If D₅ (f_(w)·f_(t))^(1/2) exceeds the upper limit of condition (24), coma in theperipheral part of the image plane suddenly increases, since theoff-axis light beam passing through fifth lens group G5 and sixth lensgroup in the wide-angle state deviates from the optical axis.Conversely, if D₅ /(f_(w) ·f_(t))^(1/2) falls below the lower limit ofcondition (24), the refractive power of fourth lens group G4 and fifthlens group G5 strengthens toward the positive. Thus, the fluctuations ofoff-axis aberrations generated as the lens positional state changes canno longer be satisfactorily corrected.

Accordingly, increased optical performance cannot be achievedsimultaneously with increased aperture size and an increased zoom ratiosince, with a four-group type zoom lens having a conventionalpositive-negative-positive-positive arrangement of refractive powers,the lateral magnification of second lens group G2 changes greatly as thelens positional state changes.

In the zoom lens of the seventh preferred embodiment of the presentinvention, increased optical performance can also be achievedsimultaneously by arranging imagewise of first lens group G1, the twonegative lenses of second lens group G2, and third lens group G3.However, to obtain improved optical performance, it is preferable tosatisfy the design condition

    0.02<Δ2/(|f.sub.2 |+|f.sub.3 |)<0.18(f.sub.2 <0, f.sub.3 <0)                  (25)

wherein Δ2 is the axial extent of change in the air space between secondlens group G2 and third lens group G3 when changing the lens positionalstate from the wide-angle state to the telephoto state. Condition (25)stipulates the focal length of second lens group G2 and third lens groupG3. If Δ2/(|f₂ |+|f₃ |) exceeds the upper limit of condition (25), thefluctuation of coma with field angle increases, since the off-axis lightbeam passing through second lens group G2 and third lens group G3 in thewide-angle state approaches the optical axis. Conversely, if Δ2/(|f₂|+|f₃ |) falls below the lower limit, coma in the peripheral part of theimage plane cannot be satisfactorily corrected, since the off-axis lightbeam passing through first lens group G1 in the telephoto state deviatesfrom the optical axis.

Now described is a zoom lens according to an eighth preferred embodimentof the present invention, which has the same lens group arrangement asthe third preferred embodiment described above with reference to zoomlens 35 of FIG. 6. In the eighth preferred embodiment, first lens groupG1 and fourth lens group G4 are fixed (i.e., do no move axially) duringzooming. Thus, the air space between second lens group G2 and third lensgroup G3 widens as these lens groups move imagewise. Also, fifth lensgroup G5 moves objectwise. Based on this configuration, the coexistenceof an increased zoom ratio and an increased aperture size is attained.

It has been known in the design of zoom lenses that if the number ofaberration correction degrees of freedom could be increased, andincreased variable power and an increased aperture size along withincreased optical performance could be achieved by increasing the numberof moveable lens groups. Nevertheless, when the number of movable lensgroups is increased, the predetermined optical performance cannot beguaranteed during manufacturing due to stringent requirements on theaccuracy of the lens stopping position. Also, there are prior artfour-group type zoom lenses having a positive-negative-positive-positivefour-group arrangement with a wide-angle field angle exceeding 70°attained by moving first lens group G1. However, since first lens groupG1 is removed from the image plane, the diameter of this lens group waslarge. Consequently, a large driving power was necessary to drive thisfirst lens group axially as the lens positional state changed.

In the zoom lens of the eighth preferred embodiment of the presentinvention, a field angle exceeding 70° can be achieved while maintaininghigh optical performance, without having to axially move first lensgroup G1. This is accomplished by arranging two negative lens groupsimagewise of first lens group G1. In addition, the predetermined zoomratio can be ensured, without simultaneously moving fourth lens group G4axially. This is accomplished by moving fifth lens group G5 axially tocompensate for the image plane movement generated as second lens groupG2 and third lens group move. Also, it is preferable to further arrangea sixth lens group imagewise of fifth lens group G5 to realize a higheroptical performance. Accordingly, if the air space between fifth lensgroup G5 and sixth lens group is changed when the lens positional statechanges, the fluctuations of off-axis aberrations generated as the lenspositional state changes can be satisfactorily corrected. To simplifythe construction of the barrel, it is preferable to locate the aperturestop between third lens group G3 and fourth lens group G4, and to setthe aperture stop at a fixed position along the optical axis, regardlessof any change in the lens positional state.

The zoom lens of the eighth preferred embodiment of the presentinvention preferably satisfies design condition (26) directed toshortening the overall length of the lens and achieving a zoom lens withsuperior portability. Condition (26) is expressed as

    1.0<f.sub.1 /(f.sub.w ·f.sub.t).sup.1/2 <1.8      (26)

If f₁ /(f_(w) ·f_(t))^(1/2) exceeds the upper limit of condition (26),the overall length of the lens in the telephoto state increases andportability suffers, since the convergence action of first lens group G1weakens. Conversely, if f₁ /(f_(w) ·f_(t))^(1/2) falls below the lowerlimit of condition (26), the off-axis light beam passing through firstlens group G1 in the wide-angle state deviates from the optical axis,and excessive coma is present in the peripheral part of the image plane.

To realize a high optical performance even with a large aperture ratioand a more compact size, it is preferable that the eighth preferredembodiment of the present invention satisfy design condition (27),expressed as

    1.5<M.sub.1 /M.sub.4 <2                                    (27)

wherein M₁ is the axial separation between the most objectwise lenssurface of first lens group G1 and the image plane, and M₄ is the axialseparation between the most objectwise lens surface of fourth lens groupG4 and the image plane.

If M₁ /M₄ exceeds the upper limit of condition (27), the off-axis lightbeam passing through second lens group G2 from first lens group G1 inthe wide-angle state deviates from the optical axis, and coma generatedwith respect to the lower part light beam at the peripheral part of theimage plane increases. Accordingly, the predetermined opticalperformance cannot be satisfied. Conversely, if M₁ /M₄ falls below thelower limit of condition (27), the fluctuation of off-axis aberrationsgenerated as the lens positional state changes cannot be satisfactorilycorrected, since the amount of movement of second lens group G2 andthird lens group when the lens positional state changes decreases.

Accordingly, in the seventh and eighth preferred embodiments of thepresent invention, it is preferable to adopt either an appropriate innerfocus (IF) system or a rear focus (RF) system for autofocusing, asdiscussed above. In particular, it is preferable to make third lensgroup G3 the focusing group. Also as discussed above, third lens groupG3 and fourth lens group G4 in the seventh and eighth preferredembodiment of the present invention principally correct off-axisaberrations. This is because, since third lens group G3 and fourth lensgroup are positioned near the center of the zoom lens, the off-axislight beam passes therethrough near the optical axis. This reducesoff-axis aberrations. Accordingly, even if third lens group G3 or fourthlens group is made the focusing group, the change in off-axisaberrations is small because the fluctuation of off-axis aberrationsgenerated when focusing at close range is small. In particular, in theseventh and eight preferred embodiment of the present invention, it ispreferable to reduce the lens diameter of the third lens group and tomake it the focusing group, since the on-axis light beam diverges fromthe third lens group and impinges on the fourth lens group. Furthermore,it is preferable to clarify the aberration correction role of each lensgroup and to locate the aperture stop between the third lens group andfourth lens group, since the third lens group and fourth lens groupprincipally correct on-axis aberration. Accordingly, with regard to thelocation of the aperture stop when changing the lens positional stateattendant with zooming, there are leases wherein the aperture stop isfixed regardless of the lens positional state. There are also caseswherein it moves together with other lens groups. To simplify theconstruction of the barrel, it is preferable that the aperture stop havea fixed position regardless of the lens positional state. Also, it ispreferable, to attain increased optical performance, that the aperturestop move together with fourth lens group G4 when the lens positionalstate changes.

A zoom lens according to a ninth preferred embodiment of the presentinvention having the same lens group configuration as the eighthpreferred embodiment described above (see, e.g., zoom lens 35 of FIG. 6)is now discussed. When the lens positional state changes from thewide-angle state to the telephoto state, at least the second lens groupmoves imagewise and at least one of first lens group G1 and fourth lensgroup G4 moves such that the space between first lens group G1 andsecond lens group G2 increases, the air space between second lens groupG2 and third lens group G3 increases, the air space between third lensgroup G3 and fourth lens group G4 decreases, and the air space betweenfourth lens group G4 and fifth lens group G5 decreases. An aperture stopis preferably located between first lens group G1 and fifth lens groupG5.

In the configuration of the ninth preferred embodiment, fifth lens groupG5 comprises, objectwise to imagewise, a positive lens subgroupincluding at least one positive lens component. Also included is anegative lens subgroup comprising a negative lens component and apositive lens component arranged in the air space imagewise of thenegative lens component. The fifth lens group G5 satisfies the designcondition

    0.15<(r.sub.1 +r.sub.2)/(r.sub.1 -r.sub.2)<1.2             (28)

wherein r₁ is the radius of curvature of the objectwise lens surface ofthe positive lens component of the negative lens subgroup, and r₂ is theradius of curvature of the lens surface imagewise of the positive lenscomponent of the negative lens subgroup. Condition (28) stipulates theshape of the most imagewise positive lens in the positive lens subgroupof fifth lens group G5.

If (r₁ +r₂)/(r₁ -r₂) exceeds the upper limit of condition (28),outward-oriented coma is generated in the wide-angle state. Conversely,if (r₁ +r₂)/(r₁ -r₂) falls below the lower limit of condition (28),inward-oriented coma is generated in the wide-angle state. In addition,it is preferable to adopt an appropriate inner focus system or rearfocus system for autofocusing, as discussed above. In particular, it ispreferable that only third lens group G3 move axially during focusing.

In the ninth preferred embodiment of the zoom lens of the presentinvention, the fluctuation of off-axis aberrations generated as the lenspositional state changes is satisfactorily corrected by locating theaperture stop near the center of the zoom lens, as explained above inconnection with the seventh preferred embodiment of the presentinvention. Aberration fluctuations are also corrected by designing thezoom trajectory of the lens groups such that the air space adjacent theaperture stop increases greatly when the lens positional state changes.In other words, in the zoom lens of the ninth preferred embodiment ofthe present invention, the coexistence of increased variable power andan increased optical performance is attained by locating the aperturestop between first lens group G1 and fifth lens group G5, and morepreferably near the center of the zoom lens.

The aberration correction function of each lens group comprising thezoom lens according to the ninth preferred embodiment of the presentinvention is now described. First lens group G1, second lens group G2and third lens group G3 are arranged close together and have a stronglynegative composite refractive power in the wide-angle state. Asufficient back focus is obtained, with the arrangement of refractivepowers of the entire lens system as a reverse telephoto system, bywidening the air space between third lens group G3 and fourth lens groupG4. If the field angle exceeds 70° is covered, it is important that thefluctuation of coma with field angle be satisfactorily corrected. Comain the lower part light beam at second lens group G2 and third lensgroup G3 is satisfactorily corrected, and coma in the upper part lightbeam at fifth lens group G5 is satisfactorily corrected by appropriatelysetting the lens group spacing such that the off-axis light beam passingthrough second lens group G2, third lens group G3 and fifth lens groupG5 in the wide-angle state deviates from the optical axis. Inparticular, it is preferable to appropriately set the focal length ofsecond lens group G2 and third lens group G3 as discussed below, toarrange first lens group G1 and second lens group G2 such that they areclose to one another, and to ensure that the off-axis light beam passingthrough first lens group G1 does not deviate excessively from theoptical axis.

The convergence action due to first lens group G1 in the telephoto stateis strengthened and the overall length of the lens is shortened byaxially moving at least second lens group G2 imagewise such that the airspace between first lens group G1 and second lens group G2 widens whenthe lens positional state changes from the wide-angle state to thetelephoto state. Also, the size of the lateral magnification of secondlens group G2 and third lens group G3 increases and the zoom ratioincreases by moving second lens group G2 and third lens group G3imagewise, and by narrowing the air space between third lens group G3and the aperture stop such that the air space between second lens groupG2 and third lens group G3 widens when the lens positional state changesfrom the wide-angle state to the telephoto state. In addition, theoff-axis light beam passing through second lens group G2 and third lensgroup G3 approaches the optical axis, and the fluctuation of off-axisaberrations as the lens positional state changes is satisfactorilycorrected.

Further, by narrowing the air space between fourth lens group G4 andfifth lens group G5 when the lens positional state changes from thewide-angle state to the telephoto state, the off-axis light beam in thewide-angle state passes through fifth lens group G5 removed from theoptical axis. The off-axis light beam approaches the optical axis as thetelephoto state is approached, and the fluctuation of off-axisaberrations generated when the lens positional state changes issatisfactorily corrected.

To realize increased aperture size, it is important that the off-axisaberrations generated by each lens group be satisfactorily corrected. Inthe zoom lens according to the ninth preferred embodiment of the presentinvention, third lens group G3 and fourth lens group G4 principallycorrect on-axis aberrations. Since third lens group G3 and fourth lensgroup G4 are positioned near the center of the zoom lens, and are morepreferably arranged relatively near the aperture stop, the off-axislight beam has a tendency to pass through these lens groups near theoptical axis. Hence, the generation of off-axis aberrations is small. Bysatisfactorily correcting off-axis aberrations generated by third lensgroup G3 and fourth lens group G4, the fluctuation of off-axisaberrations generated as the lens positional state changes can besatisfactorily corrected and an increased aperture size can be achieved.

As explained above, in the zoom lens of the ninth preferred embodimentof the present invention, the aberration correction function of eachlens group is clarified, and the coexistence of an increased zoom ratioand an increased aperture size is realized by satisfactorily correctingaberrations generated by each lens group. In addition, the diameter ofthe mount (i.e. flange) of the barrel of an interchangeable lens for asingle lens reflex (SLR) camera is fixed. Thus, the diameter of the mostimagewise lens is constrained. Generally, this most imagewise lens has apositive refractive power and the aperture stop is located objectwise ofthe most imagewise lens group. Accordingly, the diameter of the mostimagewise lens tends to increase if the back focus shortens. In theprior art, a negative lens is frequently the most imagewise lens, suchas is disclosed in Japanese Patent Application Kokai No. Hei 6-34885.

In the zoom lens of the ninth preferred embodiment of the presentinvention, fifth lens group G5 comprises a positive lens subgroup havingat least one positive lens, and a negative lens subgroup having anegative lens and a positive lens arranged imagewise thereof. Based onthis configuration, the off-axis light beam passing through the mostimagewise lens approaches the optical axis. Consequently, satisfactoryimage optical performance and compactness are possible with a smallnumber of constituent lenses.

In the ninth preferred embodiment of the present invention, the off-axislight beam passes through third lens group G3 and fourth lens group G4near the optical axis by virtue of being near the center of the zoomlens. Accordingly, the generation of off-axis aberrations is small, andthird lens group G3 and fourth lens group G4 principally correct on-axisaberrations. Also, the change in off-axis aberrations is small even ifthird lens group G3 and fourth lens group G4 move axially. Consequently,if third lens group G3 is made the focusing group, increased opticalperformance is possible since the fluctuation of off-axis aberrationsgenerated when focusing at close range is small. In particular, sincethe on-axis light beam diverges from third lens group G3 and impinges onfourth lens group G4, the lens diameter of third lens group G3 issmaller. As such, it is preferable to make third lens group G3 thefocusing group. In addition, it is preferable to clarify the aberrationcorrection role of each lens and to locate the aperture stop betweenthird lens group G3 and fourth lens group G4, since third lens group G3and fourth lens group G4 principally correct on-axis aberrations.

With respect to aperture stop location, the case wherein the aperturestop is fixed regardless of the lens positional state, and the casewherein it moves together with another lens group are known. In the zoomlens of the ninth preferred embodiment of the present invention, incertain cases it is preferable that the aperture stop be at a fixedposition regardless of the lens positional state to simply the lensbarrel construction. In other cases, it is preferable that the aperturestop move together with the fourth lens group when the lens positionalstate changes to increase optical performance.

It is also preferable that the zoom lens of the ninth preferredembodiment of the present invention satisfy the design condition

    0.75<|f.sub.b |/f.sub.5 <1.50            (29)

wherein f_(b) is the focal length of the negative lens subgroup of fifthlens group G5. Condition (29) stipulates an appropriate focal length forthe negative lens subgroup of fifth lens group G5 for increasingcompactness, performance and balance. If |f_(b) |/f₅ exceeds the upperlimit of condition (29), the overall length of the lens in the telephotostate cannot be reduced. Conversely, if |f_(b) |/f₅ falls below thelower limit of condition (29), the off-axis light beam passing throughfifth lens group G5 in the wide-angle state approaches the optical axisand the fluctuation in coma with field angle cannot be satisfactorilycorrected.

The zoom lens of the ninth preferred embodiment of the present inventionpreferably also satisfies the design condition

    0.2<(f.sub.4 -f.sub.5)/(f.sub.4 +f.sub.5)<0.2.             (30)

Condition (30) stipulates an appropriate ratio between the focal lengthsof fourth lens group G4 and fifth lens group G5. If (f₄ -f₅)/(f₄ +f₅)exceeds the upper limit of condition (30), the off-axis light beampassing through the fifth lens group in the wide-angle state approachesthe optical axis. As such, the fluctuation of coma with field anglecannot be satisfactorily corrected. Conversely, if (f₄ -f₅)/(f₄ +f₅)falls below the lower limit of condition (30), negative sphericalaberration generated by the fourth lens group increases, and thefluctuations in on-axis aberrations are generated as the lens positionalstate changes.

The zoom lens of the ninth preferred embodiment of the present inventionalso preferably satisfies the design condition

    2.5<f.sub.1 /|f.sub.2 |<3.5.             (31)

Condition (31) stipulates an appropriate ratio for the focal lengths offirst lens group G1 and second lens group G2 for increasing thecompactness of the zoom lens. If f₁ /|f₂ | exceeds the upper limit ofcondition (31), the overall length of the lens in the telephoto stateincreases. Conversely, if f₁ /|f₂ | falls below the lower limit ofcondition (31), the off-axis light beam passing through first lens groupG1 deviates from the optical axis, causing the lens diameter toincrease.

The zoom lens of the ninth preferred embodiment of the present inventionalso preferably satisfies the design condition

    -0.5<(f.sub.2 -f.sub.3)/(f.sub.2 +f.sub.3)<0.              (32)

Condition (32) stipulates an appropriate range for the focal lengths ofsecond lens group G2 and third lens group G3, and is necessary forattaining the coexistence of increased zoom ratio and increased opticalperformance. If (f₂ -f₃)/(f₂ +f₃) exceeds the upper limit of condition(32), positive spherical aberration generated by third lens group G3cannot be satisfactorily corrected. Conversely, if (f₂ -f₃)/(f₂ +f₃)falls below the lower limit of condition (32), the off-axis light beampassing through second lens group G2 in the wide-angle state approachesthe optical axis, and the fluctuation of coma with field angle cannot besatisfactorily corrected.

The zoom lens of the ninth preferred embodiment of the present inventionalso preferably satisfies the design condition

    f.sub.1 /|f.sub.12t |<0.6                (33)

wherein f_(12t) is the composite focal length of first lens group G1 andsecond lens group G2 in the telephoto state. Design condition (33)stipulates the lateral magnification of third lens group G3 in thetelephoto state and is necessary for reducing the amount of lensmovement if third lens group G3 is made the focusing group. If f_(t)/|f_(12t) | exceeds the upper limit of condition (33), the amount ofaxial movement when focusing at close range is extremely large, sincethe lateral magnification of third lens group G3 increases. Furthermore,in the Working Examples of the present invention set forth below, anaperture ratio on the order of FNO 2.8 is realized. However, it isstraightforward, for example, to reduce the zoom ratio and increase theaperture ratio, or to increase the FNO and increase the zoom ratio.

To prevent image blurring caused by hand vibration and the like, whichtends to occur when taking a photo with a high zoom ratio zoom lenses,it is possible to include with each preferred embodiment of the presentinvention, as discussed above, an antivibration optical system. This isaccomplished by first providing a blur detection system that detectsblurring, and a driving means for shifting (i.e., driving) all or partof one lens group as an eccentric lens group. Then, detecting blurringby the blur detection system and shifting the image by shifting theeccentric lens group by the drive means so that the detected blurring iscorrected.

In addition, the zoom lens of the present invention can be applied notonly to a zoom lens that continuously changes the focal length whilemaintaining a fixed image plane position, but also to a varifocal lenswherein the image plane position fluctuates when continuously changingthe focal length, or to a so-called step zoom lens that changes thefocal length in steps, rather than continuously.

Working Examples

Set forth below are 16 Working Examples of the zoom lenses of thepresent invention as described above. In each Working Example, theaspherical surface is expressed by the following numerical expression(d):

    S(y)=(y.sup.2 /R)/{1+(1-κ·y.sup.2 /R.sup.2).sup.1/2 }+C4·y.sup.4 +C6·y.sup.6 +C8·y.sup.8 +C10·y.sup.10 +                                  (d)

wherein y is the height in the direction perpendicular to the opticalaxis, S(y) is the deflection amount (sag amount) in height y, R is thereference radius of curvature (vertex radius of curvature), K is theconical coefficient, and Cn is the nth order aspherical coefficient.

Tables 1a-d through 16a-d list the design values and design conditionsfor Working Examples 1-16, respectively. In the Tables, f is the focallength, FNO is the f-number, 2 φ is the field angle, φ is the aperturestop radius, and Bf is the back focus. Also, S is the surface number, ris the radius of curvature, d is the axial distance between surfaces, nis the index of refraction with respect to the d-line (λ=587.6 nm), andv is the Abbe number. Aberration plots are provided for Working Example1 to show the degree of aberration correction. Such aberration plots areeasily generated for Working Examples 2-16 from the corresponding designtables. The data for the aspherical surfaces are provided in Tables1b-16b. In addition, a radius of curvature of "∞" indicates a planesurface.

Working Examples 1-3

As shown in FIG. 1, the zoom lens 10 represents to Working Examples 1-3of the present invention and comprises, from object plane 12 to imageplane 14 along optical axis 16, a first lens group G1 having a positiverefractive power, second lens group G2 having a negative refractivepower, third lens group G3 having a negative refractive power, fourthlens group G4 having a positive refractive power, fifth lens group G5having a positive refractive power, and sixth lens group G6 having anegative refractive power.

When performing the focal length variable operation (zooming) from thewide-angle positional state to the telephoto positional state, at leastsecond lens group G2 moves imagewise and sixth lens group G6 movesobjectwise such that the air space between first lens group G1 andsecond lens group G2 increases, the air space between second lens groupG2 and third lens group G3 increases, the air space between third lensgroup G3 and fourth lens group G4 decreases, the air space betweenfourth lens group G4 and fifth lens group G5 decreases, and the airspace between fifth lens group G5 and sixth lens group G6 changes.

Working Example 1

FIG. 2 shows the configuration of a zoom lens 20 according to WorkingExample 1 of the present invention. Zoom lens 20 comprises, from objectplane 12 to image plane 14 along optical axis 16 (i.e., objectwise toimagewise), first lens group G1 comprising objectwise to imagewise, anegative meniscus lens L11 having an objectwise convex surface, abiconvex lens L12, and positive meniscus lens L13 having an objectwiseconvex surface. Second lens group G2 comprises, objectwise to imagewise,a negative meniscus lens L21 having an objectwise convex surface, and anegative cemented lens L22 having a biconcave lens L22a and a biconvexlens L22b. Third lens group G3 comprises, objectwise to imagewise, anegative cemented lens L3 having a biconcave lens L3a and a positivemeniscus lens L3b having an objectwise convex surface. Fourth lens groupG4 comprises, objectwise to imagewise, a biconvex lens L41, a biconvexlens L42, and negative meniscus lens L43 having an objectwise concavesurface. Fifth lens group G5 comprises, objectwise to imagewise, abiconvex lens L51, a biconvex lens L52, a biconcave lens L53, and abiconvex lens L54. Sixth lens group G6 comprises a negative meniscuslens L6 having an objectwise concave surface.

In Working Example 1, when varying power (zooming) from the wide-anglestate to the telephoto state, first lens group G1 first moves imagewiseand then moves objectwise, second lens group G2 and third lens group G3move imagewise, and fourth lens group G4 to sixth lens group G6 moveobjectwise. Thus, the air space between first lens group G1 and secondlens group G2 increases, the air space between second lens group G2 andthird lens group G3 increases, the air space between third lens group G3and fourth lens group G4 decreases, the air space between fourth lensgroup G4 and fifth lens group G5 decreases, and the air space betweenfifth lens group G5 and sixth lens group G6 first increases and thendecreases. In addition, an aperture stop AS is located adjacent fourthlens group G4 between third lens group G3 and fourth lens group G4, andmoves together with fourth lens group G4. Further, the aperture stopradius increases when zooming from the wide-angle state to the telephotostate.

Tables 1a-d list the design values and design conditions for WorkingExample 1 of the present invention.

                  TABLE 1a                                                        ______________________________________                                        DESIGN TABLE                                                                  ______________________________________                                        f          28.80     70.00     140.00  194.00                                 FNO        2.90      2.90      2.90    2.90                                   2ω   75.65     33.15     16.95   12.22°                          Aperture Diameter                                                                        26.00     32.24     35.22   35.40                                  ______________________________________                                        S          r         d         n       ν                                    1         161.8062  1.500     1.84666 23.83                                   2         76.7425   1.000                                                     3         76.9182   9.900     1.62041 60.35                                   4         -1133.1769                                                                              0.100                                                     5         70.9581   6.700     1.69350 53.31                                   6         253.4789  (d6 =                                                                         variable)                                                 7         1674.5951 1.200     1.81474 37.03                                   8         30.4350   7.750                                                     9         -200.8124 0.900     1.83500 42.97                                  10         41.4244   5.700     1.84666 23.83                                  11         -168.3388 (d11 =                                                                        variable)                                                12         -52.6800  1.000     1.67003 47.19                                  13         42.4871   3.800     1.84666 23.83                                  14         169.5940  (d14 =                                                                        variable)                                                15         ∞   0.700     Aperture                                                                      stop                                           16         61.5342   4.900     1.49782 82.52                                  17         -197.1872 0.100                                                    18         64.2715   5.000     1.49782 82.52                                  19         -193.6733 1.300                                                    20         -87.4033  0.800     1.83400 37.35                                  21         -6013.1438                                                                              (d21 =                                                                        variable)                                                22         66.9795   4.300     1.69680 55.48                                  23         -153.7929 9.200                                                    24         78.6865   9.100     1.49782 82.52                                  25         -41.1071  0.100                                                    26         -160.5423 1.000     1.82027 29.69                                  27         31.3268   6.450                                                    28         110.2877  4.700     1.71736 29.50                                  29         -70.1805  (d29 =                                                                        variable)                                                30         -38.0379  1.000     1.83500 42.97                                  31         -59.0360  (Bf)                                                     ______________________________________                                    

                                      TABLE 1b                                    __________________________________________________________________________    ASPHERIC COEFFICIENTS                                                         __________________________________________________________________________    S7  r = 1674.5951                                                                             κ = 5.5228                                                                          C.sub.4  = +1.23744 × 10.sup.-6             /// C.sub.6  = -7.80256 × 10.sup.-10                                                    C.sub.8  = +4.36329 × 10.sup.-13                                                    C.sub.10  = -9.00276 × 10.sup.-15           S22 r = 66.9795 κ = 2.3824                                                                          C.sub.4  = -5.00920 × 10.sup.-6             /// C.sub.6  = -2.89371 × 10.sup.-9                                                     C.sub.8  = +1.16663 × 10.sup.-12                                                    C.sub.10  = -9.00276 × 10.sup.-15           __________________________________________________________________________

                  TABLE 1c                                                        ______________________________________                                        VARIABLE SPACING WHEN VARYING POWER (ZOOMING)                                 FOCUSED ON OBJECT AT ∞                                                  Lens Position                                                                            a         b       c        d                                       ______________________________________                                        f          28.8000   70.0000 140.0007 194.0017                                d6         1.5000    22.4101 40.6790  47.9809                                 d11        4.6623    5.4954  5.4954   12.3558                                 d14        48.9055   21.7913 9.6248   1.7500                                  d21        28.7619   10.0340 2.4570   1.0000                                  d29        2.9672    4.3268  5.0384   4.3105                                  Bf         38.0002   60.7400 68.1438  69.4049                                 ______________________________________                                    

                  TABLE 1d                                                        ______________________________________                                        DESIGN CONDITION VALUES                                                       ______________________________________                                                  f.sub.1  = 100.5335                                                           f.sub.2  = -41.1088                                                           f.sub.3  = -73.2715                                                           f.sub.4  = 82.6660                                                            f.sub.5  = 57.2137                                                            (1) f.sub.1 /(f.sub.w  · f.sub.t).sup.1/2  = 1.345                   (2) TL.sub.w /TL.sub.t  = 0.947                                               (3) D.sub.34 /f.sub.w  = 1.698                                                (4) D.sub.12 /f.sub.t  = 0.247                                                (5) D.sub.45 /f.sub.5  = 0.503                                                (6) f.sub.3 /f.sub.2  = 1.782                                                 (7) f.sub.4 /f.sub.5  = 1.445                                       ______________________________________                                    

FIGS. 3A(I)-3A(IV), 3B(I)-3B(IV), 3C(I)-3C(IV) and 3D(I)-3D(IV) areaberration plots of Working Example 1 with respect to the d-line(λ=587.6 nm)(infinite focus) for zoom lens 20 in the wide-angle state(f=28.8), in a first intermediate focal length state (f=70.0), in asecond intermediate focal length state (f=140.0), state in the telephotostate (f=194.0), respectively. In each aberration plot, Y is the imageheight, and A is the half field angle with respect to each image height.In the aberration plots for astigmatism (3A(II)-3D(II)), the solid lineindicates the sagittal image plane, and the broken line indicates themeridional image plane. In the aberration plots for spherical aberration(3A(I)-3D(I)), the broken line indicates the sine condition.

As is clear from the aberration plots, the various aberrations in eachfocal length state spanning from the wide-angle state to the telephotostate are satisfactorily corrected, and excellent image formationperformance is achieved. This degree of aberration correction is alsorepresentative of Working Examples 2-16, below.

Working Example 2

FIG. 4 shows the configuration of a zoom lens 25 according to WorkingExample 2 of the present invention. Zoom lens 25 has the same basicconfiguration as zoom lens 20 of FIG. 2 combined to form (WorkingExample 1), except that lenses 42 and 43 in zoom lens 20 are, in zoomlens 25, compound lens 42 comprising lenses 42a and 42b. Also, zoom lens25 undergoes the same changes in the air spaces when zooming as zoomlens 20.

Tables 2a-d list the design values and design conditions for WorkingExample 2 of the present invention.

                  TABLE 2a                                                        ______________________________________                                        DESIGN TABLE                                                                  ______________________________________                                        f          28.80     70.00     140.00  194.00                                 FNO        2.90      2.90      2.90    2.90                                   2ω   75.41     33.05     16.88   12.24°                          Aperture Diameter                                                                        25.60     31.48     33.84   35.34                                  ______________________________________                                        S          r         d         n       ν                                   ______________________________________                                         1         190.4150  1.500     1.84666 23.83                                   2         85.9379   1.000                                                     3         84.7483   9.800     1.62041 60.35                                   4         -423.7788 0.100                                                     5         69.0744   6.000     1.69680 55.48                                   6         171.7412  (d6 =                                                                         variable)                                                 7         393.1037  1.200     1.81474 37.03                                   8         31.5103   7.750                                                     9         -160.2839 0.900     1.83500 42.97                                  10         46.1305   5.350     1.84666 23.83                                  11         -163.1180 (d11 =                                                                        variable)                                                12         -51.0866  1.000     1.65844 50.84                                  13         44.3577   3.550     1.84666 23.83                                  14         167.0177  (d14 =                                                                        variable)                                                15         ∞   0.700     Aperture                                                                      stop                                           16         65.6168   4.100     1.49782 82.52                                  17         -371.0737 0.100                                                    18         66.7445   6.850     1.49782 82.52                                  19         -57.3842  1.000     1.83500 42.97                                  20         -904.8357 (d20 =                                                                        variable)                                                21         79.3307   3.350     1.74330 49.23                                  22         -203.2664 9.900                                                    23         86.2312   9.050     1.49782 82.52                                  24         -40.8025  0.100                                                    25         254.6695  1.000     1.80518 25.46                                  26         29.2625   7.050                                                    27         106.5051  3.400     1.84666 23.83                                  28         -162.0625 (d28 =                                                                        variable)                                                29         -46.2971  1.000     1.83500 42.97                                  30         -86.4862  (Bf)                                                     ______________________________________                                    

                                      TABLE 2b                                    __________________________________________________________________________    ASPHERIC COEFFICIENTS                                                         __________________________________________________________________________    S7  r = 393.1037                                                                              κ = 11.0000                                                                         C.sub.4  = + 7.64647 × 10.sup.-7            /// C.sub.6  = -5.49504 × 10.sup.-10                                                    C.sub.8  = +2.33357 × 10.sup.-13                                                    C.sub.10  = +1.04457 × 10.sup.-16           S21 r = 79.3307 κ = 2.2669                                                                          C.sub.4  = -5.18000 × 10.sup.-6             /// C.sub.6  = -2.51053 × 10.sup.-9                                                     C.sub.8  = -9.16437 × 10.sup.-13                                                    C.sub.10  = -5.29344 × 10.sup.-15           __________________________________________________________________________

                  TABLE 2c                                                        ______________________________________                                        VARIABLE SPACING WHEN VARYING POWER (ZOOMING)                                 FOCUSED ON OBJECT AT ∞                                                  Lens Position                                                                            a         b       c        d                                       ______________________________________                                        f          28.8000   70.0000 140.0007 194.0017                                d6         1.5000    23.8936 43.5476  49.4290                                 d11        4.7922    6.9315  8.4315   11.5431                                 d14        50.0388   21.8953 9.3535   1.7500                                  d20        31.0173   11.5624 4.5146   1.4000                                  d28        3.4633    4.3268  4.8912   4.1799                                  Bf         37.9997   59.9569 65.9685  70.9484                                 ______________________________________                                    

                  TABLE 2d                                                        ______________________________________                                        DESIGN CONDITION VALUES                                                       ______________________________________                                                  f.sub.1  = 104.4695                                                           f.sub.2  = -43.5791                                                           f.sub.3  = -72.4370                                                           f.sub.4  = 85.3736                                                            f.sub.5  = 55.8498                                                            (1) f.sub.1 /(f.sub.w  · f.sub.t).sup.1/2  = 1.398                   (2) TL.sub.w /TL.sub.t  = 0.954                                               (3) D.sub.34 /f.sub.w  = 1.737                                                (4) D.sub.12 /f.sub.t  = 0.255                                                (5) D.sub.45 /f.sub.5  = 0.555                                                (6) f.sub.3 /f.sub.2  = 1.662                                                 (7) f.sub.4 /f.sub.5  = 1.529                                       ______________________________________                                    

Working Example 3

FIG. 5 shows the configuration of a zoom lens 30 according to WorkingExample 3 of the present invention. Zoom lens 30 has the same basicconfiguration as zoom lens 25 of FIG. 4 (Working Example 2).

In Working Example 3, when zooming from the wide-angle state to thetelephoto state, first lens group G1 first moves imagewise and thenmoves objectwise, second lens group G2 and third lens group G3 moveimagewise, and fifth lens group G5 and sixth lens group G6 moveobjectwise such that the air space between first lens group G1 andsecond lens group G2 increases, the air space between second lens groupG2 and third lens group G3 increases, the air space between third lensgroup G3 and fourth lens group G4 decreases, the air space betweenfourth lens group G4 and fifth lens group G5 decreases, and the airspace between fifth lens group G5 and sixth lens group G6 firstincreases and then decreases. However, fourth lens group G4 is fixedalong the optical axis. In addition, an aperture stop AS is locatedadjacent fourth lens group G4 between third lens group G3 and fourthlens group G4. The aperture stop radius increases when zooming from thewide-angle state to the telephoto state, although it is fixed along theoptical axis together with fourth lens group G4.

Tables 3a-3d list the design values and design conditions for WorkingExample 3 of the present invention.

                  TABLE 3a                                                        ______________________________________                                        DESIGN TABLE                                                                  ______________________________________                                        f          28.80     70.00     140.00  194.00                                 FNO        2.90      2.90      2.90    2.90                                   2ω   75.59     33.05     16.92   12.25°                          Aperture Diameter                                                                        26.13     31.58     34.60   35.78                                  ______________________________________                                        S          r         d         n       ν                                   ______________________________________                                         1         176.1773  1.500     1.84666 23.83                                   2         81.5336   1.000                                                     3         80.8687   10.500    1.62041 60.35                                   4         -557.5412 0.100                                                     5         68.7958   6.450     1.69680 55.48                                   6         199.5057  (d6 =                                                                         variable)                                                 7         637.6892  1.200     1.81474 37.03                                   8         31.2514   7.950                                                     9         -144.5846 0.900     1.83500 42.97                                  10         48.1839   5.300     1.84666 23.83                                  11         -163.1988 (d11 =                                                                        variable)                                                12         -49.7238  1.000     1.62280 56.93                                  13         48.0796   3.300     1.84666 23.83                                  14         161.0550  (d14 =                                                                        variable)                                                15         ∞   0.700     Aperture                                                                      stop                                           16         68.3778   4.000     1.49782 82.52                                  17         -427.0582 0.100                                                    18         77.6111   6.950     1.49782 82.52                                  19         -52.1300  1.000     1.83500 42.97                                  20         -232.3430 (d20 =                                                                        variable)                                                21         61.6060   4.500     1.65160 58.44                                  22         -243.7490 7.700                                                    23         65.9685   12.000    1.49782 82.52                                  24         -42.5379  0.100                                                    25         -156.0129 1.000     1.80610 33.27                                  26         30.7964   5.000                                                    27         110.4314  4.550     1.74950 35.04                                  28         -72.1558  (d28 =                                                                        variable)                                                29         -38.2808  1.000     1.83500 42.97                                  30         -62.4862  (Bf)                                                     ______________________________________                                    

                                      TABLE 3b                                    __________________________________________________________________________    ASPHERIC COEFFICIENTS                                                         __________________________________________________________________________    S7  r = 637.6892                                                                              κ = 7.4504                                                                          C.sub.4  = +9.60240 × 10.sup.-7             /// C.sub.6  = -7.93770 × 10.sup.-10                                                    C.sub.8  = +7.86540 × 10.sup.-13                                                    C.sub.10  = -8.16590 × 10.sup.-16           S21 r = 61.6060 κ = 1.6361                                                                          C.sub.4  = -4.14690 × 10.sup.-6             /// C.sub.6  = -2.58840 × 10.sup.-9                                                     C.sub.8  = +5.30380 × 10.sup.-13                                                    C.sub.10  = -8.16590 × 10.sup.-15           __________________________________________________________________________

                  TABLE 3c                                                        ______________________________________                                        VARIABLE SPACING WHEN VARYING POWER (ZOOMING)                                 FOCUSED ON OBJECT AT ∞                                                  Lens Position                                                                            a         b       c        d                                       ______________________________________                                        f          28.8000   70.0000 140.0007 194.0017                                d6         1.5000    23.6870 40.9809  46.9308                                 d11        5.8385    7.3082  8.3922   11.7638                                 d14        50.3627   22.5670 9.4694   1.7500                                  d20        35.6896   13.1134 4.6612   1.4000                                  d28        3.0657    4.3377  4.8016   4.3599                                  Bf         37.9997   59.3036 67.2917  70.9942                                 ______________________________________                                    

                  TABLE 3d                                                        ______________________________________                                        DESIGN CONDITION VALUES                                                       ______________________________________                                                  f.sub.1  = 100.2638                                                           f.sub.2  = -40.5974                                                           f.sub.3  = -75.7326                                                           f.sub.4  = 82.8560                                                            f.sub.5  = 57.7304                                                            (1) f.sub.1 /(f.sub.w  · f.sub.t).sup.1/2  = 1.341                   (2) TL.sub.w /TL.sub.t  = 0.988                                               (3) D.sub.34 /f.sub.w  = 1.749                                                (4) D.sub.12 /f.sub.t  = 0.242                                                (5) D.sub.45 /f.sub.5  = 0.618                                                (6) f.sub.3 /f.sub.2  = 1.865                                                 (7) f.sub.4 /f.sub.5  = 1.435                                       ______________________________________                                    

Working Examples 4-6

Next, Working Examples 4-6 according to the present invention arediscussed. With reference to FIG. 6, zoom lens 35 according to WorkingExamples 4-6 comprises, objectwise to imagewise, a first lens group G1having a positive refractive power, second lens group G2 having anegative refractive power, third lens group G3 having a negativerefractive power, fourth lens group G4 having a positive refractivepower, and fifth lens group G5 having a positive refractive power.Accordingly, when zooming from the wide-angle state to the telephotostate, at least second lens group G2 and third lens group G3 moveimagewise, and fifth lens group G5 moves objectwise such that the airspace between first lens group G1 and second lens group G2 increases,the air space between second lens group G2 and third lens group G3increases, the air space between third lens group G3 and fourth lensgroup G4 decreases, and the air space between fourth lens group G4 andfifth lens group G5 decreases.

Working Example 4

FIG. 7 shows the configuration of a zoom lens 40 representing WorkingExample 4 of the present invention. Zoom lens 40 has the same basicconfiguration as zoom lens 35 of FIG. 6 (Working Example 3), except thatfifth lens group G5 comprises, objectwise to imagewise, a positivebiconvex lens L51, a positive biconvex lens L52, a negative meniscuslens L53 having an objectwise convex surface, a positive biconvex lensL54, and a negative meniscus lens L55 having an objectwise concavesurface. Third lens group G3 moves objectwise when focusing at closerange. Also, when zooming from the wide-angle state to the telephotostate, fourth lens group G4 is fixed along the optical axis, though thisis not necessary.

Tables 4a-4d list the design values and design conditions for WorkingExample 4 of the present invention.

                  TABLE 4a                                                        ______________________________________                                        DESIGN TABLE                                                                  ______________________________________                                        f           28.80     70.00    140.00 194.00                                  FNO         2.90      2.90     2.90   2.90                                    2ω    75.52     33.05    16.86  12.23°                           Aperture Diameter                                                                         24.60     31.14    34.46  34.88                                   ______________________________________                                        S           r         d        n      ν                                    ______________________________________                                         1          137.7212  1.500    1.84666                                                                              23.83                                    2          79.9973   1.000    1.0                                             3          78.6874   11.100   1.59319                                                                              67.87                                    4          -562.2914 0.100    1.0                                             5          76.4641   5.000    1.65160                                                                              58.44                                    6          166.1102  (D6)     1.0                                             7          277.8458  1.200    1.79450                                                                              45.50                                    8          32.3112   6.950    1.0                                             9          -408.4269 0.900    1.83500                                                                              42.97                                   10          49.5012   4.300    1.84666                                                                              23.83                                   11          ∞   (D11)    1.0                                            12          -52.3364  1.000    1.65160                                                                              58.44                                   13          47.9742   3.400    1.84666                                                                              23.83                                   14          186.2512  (D14)    1.0                                            15          ∞   0.700    1.0                                            16          75.4180   3.300    1.59319                                                                              67.87                                   17          ∞   0.100    1.0                                            18          66.9041   7.450    1.60300                                                                              65.42                                   19          -49.6620  1.000    1.83400                                                                              37.35                                   20          649.2389  (D21)    1.0                                            21          78.1592   3.400    1.74330                                                                              49.23                                   22          -204.6816 9.400    1.0                                            23          92.9839   9.900    1.49782                                                                              82.52                                   24          -39.5173  0.100    1.0                                            25          208.4392  1.000    1.80518                                                                              25.46                                   26          29.3010   6.750    1.0                                            27          88.3424   3.500    1.84666                                                                              23.83                                   28          -209.2210 3.850    1.0                                            29          -44.9630  1.000    1.80420                                                                              46.51                                   30          -82.8618  (Bf)     1.0                                            ______________________________________                                    

                                      TABLE 4b                                    __________________________________________________________________________    ASPHERIC COEFFICIENTS                                                         __________________________________________________________________________    S7  r = 11.000  C.sub.4  = 4.89570 × 10.sup.-7                                                      C.sub.6  = -1.19380 × 10.sup.-9             /// C.sub.8  = 2.06570 × 10.sup.-12                                                     C.sub.10  =-1.31260 × 10.sup.-15                        S21 r = 0.5704  C.sub.4  = -4.79240 × 10.sup.-6                                                     C.sub.6  = -2.57790 × 10.sup.-9             /// C.sub.8  = -6.26790 × 10.sup.-13                                                    C.sub.10  = -6.48330 × 10.sup.-15                       __________________________________________________________________________

                  TABLE 4c                                                        ______________________________________                                        VARIABLE SPACING WHEN VARYING POWER (ZOOMING)                                 FOCUSED ON OBJECT AT ∞                                                  Lens Position                                                                            a         b       c        d                                       ______________________________________                                        f          28.8000   70.0000 140.0007 194.0017                                D5         1.5000    24.5154 46.2698  54.0949                                 D11        6.4908    10.8471 11.8471  12.8537                                 D14        46.8960   19.3483 8.3455   1.7500                                  D21        29.2660   10.7209 4.3761   1.4799                                  Bf         38.1254   63.3850 71.2605  71.9208                                 f          28.8000   70.0000 140.0007 194.0017                                Δ3   1.9889    1.5273  2.0984   2.6559                                  ______________________________________                                    

                  TABLE 4d                                                        ______________________________________                                        DESIGN CONDITION VALUES                                                       ______________________________________                                                  f.sub.1  = 113.3303                                                           f.sub.2  = -42.0916                                                           f.sub.3  = -76.9017                                                           f.sub.4  = 88.0091                                                            f.sub.5  = 70.1403                                                            (8) (Ave. C) · f.sub.w  = 0.329                                      (9) D.sub.2 /f.sub.1  = 0.477                                                 (10) |r.sub.a |/D.sub.a  = 1.020                            (11) D.sub.5 /f.sub.w  = 0.326                                                (12) f.sub.1 /f.sub.1  = 0.584                                                (13) f.sub.3 /f.sub.2  = 1.827                                                (14) f.sub.4 /f.sub.5  = 1.255                                      ______________________________________                                    

Working Example 5

FIG. 8 shows the configuration of a zoom lens 45 according to WorkingExample 5 of the present invention. Zoom lens 45 has the same basicconfiguration as zoom lens 40 of FIG. 7 (Working Example 4). Third lensgroup G3 moves objectwise when focusing at close range.

Tables 5a-5d list the design values and design conditions for WorkingExample 5 of the present invention.

                  TABLE 5a                                                        ______________________________________                                        DESIGN TABLE                                                                  ______________________________________                                        f           28.80     70.00    140.00 194.00                                  FNO         2.90      2.90     2.90   2.90                                    2ω    75.53     33.05    16.87  12.24°                           Aperture Diameter                                                                         24.64     31.54    34.58  35.04                                   ______________________________________                                        S           r         d        n      ν                                    ______________________________________                                         1          142.5080  1.500    1.84666                                                                              23.83                                    2          80.2558   1.000    1.0                                             3          78.7991   10.900   1.60300                                                                              65.42                                    4          -545.8065 0.100    1.0                                             5          76.2358   4.900    1.67790                                                                              55.52                                    6          156.1563  (D6)     1.0                                             7          283.6650  1.200    1.79450                                                                              45.50                                    8          31.9413   6.900    1.0                                             9          -484.3823 0.900    1.83500                                                                              42.97                                   10          51.0355   4.200    1.84666                                                                              23.83                                   11          ∞   (D11)    1.0                                            12          -50.5493  1.000    1.65160                                                                              58.44                                   13          49.4874   3.500    1.84666                                                                              23.83                                   14          207.7760  (D14)    1.0                                            15          ∞   0.700    1.0                                            16          76.9503   3.400    1.61800                                                                              63.39                                   17          1359.3209 0.100    1.0                                            18          62.7412   7.200    1.49782                                                                              82.52                                   19          -56.8763  1.000    1.83400                                                                              37.35                                   20          1509.2003 (D21)    1.0                                            21          77.6758   3.550    1.74330                                                                              49.23                                   22          -197.2597 9.700    1.0                                            23          90.5823   9.400    1.49782                                                                              82.52                                   24          -40.3677  0.100    1.0                                            25          221.5655  1.000    1.80518                                                                              25.46                                   26          29.1464   7.050    1.0                                            27          88.1519   3.600    1.84666                                                                              23.83                                   28          -208.3678 3.800    1.0                                            29          -45.5235  1.000    1.80420                                                                              46.51                                   30          -83.0370  (Bf)     1.0                                            ______________________________________                                    

                                      TABLE 5b                                    __________________________________________________________________________    ASPHERIC COEFFICIENTS                                                         __________________________________________________________________________    S7  r = -9.000  C.sub.4  = 7.00492 × 10.sup.-7                                                      C.sub.6  = -1.14589 × 10.sup.-9             /// C.sub.8  = 1.86951 × 10.sup.-12                                                     C.sub.10  = -1.13237 × 10.sup.-15                       S21 r = 1.1300  C.sub.4  = -4.86747 × 10.sup.-6                                                     C.sub.6  = -2.40966 × 10.sup.-9             /// C.sub.8  = -7.06837 × 10.sup.-13                                                    C.sub.10  = -5.58542 × 10.sup.-15                       __________________________________________________________________________

                  TABLE 5c                                                        ______________________________________                                        VARIABLE SPACING WHEN VARYING POWER (ZOOMING)                                 FOCUSED ON OBJECT AT ∞                                                  Lens Position                                                                            a         b       c        d                                       ______________________________________                                        f          28.8000   70.0000 140.0000 194.0000                                D5         1.5000    24.7479 46.6978  54.5403                                 D11        6.4854    10.9020 11.9019  12.6781                                 D14        46.4172   19.1023 8.2148   1.7500                                  D21        28.6418   10.2920 4.0519   1.1000                                  Bf         38.0000   63.4464 71.4325  72.2311                                 f          28.8000   70.0000 140.0000 194.0000                                Δ3   1.9554    1.5011  2.0622   2.6011                                  ______________________________________                                    

                  TABLE 5d                                                        ______________________________________                                        DESIGN CONDITION VALUES                                                       ______________________________________                                                  f.sub.1  = 113.7726                                                           f.sub.2  = -42.1168                                                           f.sub.3  = -76.3735                                                           f.sub.4  = 87.5299                                                            f.sub.5  = 70.4900                                                            (8) (Ave. C) · f.sub.w  = 0.325                                      (9) D.sub.2 /f.sub.1  = 0.479                                                 (10) |r.sub.a |/D.sub.a  = 0.993                            (11) D.sub.5 /f.sub.w  = 0.337                                                (12) f.sub.1 /f.sub.1  = 0.586                                                (13) f.sub.3 /f.sub.2  = 1.813                                                (14) f.sub.4 /f.sub.5  = 1.242                                      ______________________________________                                    

Working Example 6

FIG. 9 shows the configuration of a zoom lens 50 according to WorkingExample 6 of the present invention. Zoom lens 50 has the same basicconfiguration as zoom lens 40 of FIG. 7 (Working Example 4). Third lensgroup G3 moves objectwise when focusing at close range.

Tables 6a-d list the design values and design conditions for WorkingExample 6 of the present invention.

                  TABLE 6a                                                        ______________________________________                                        DESIGN TABLE                                                                  ______________________________________                                        f           28.80     70.00    140.00 194.00                                  FNO         2.90      2.90     2.90   2.90                                    2ω    76.39     33.30    17.00  12.33°                           Aperture Diameter                                                                         24.86     32.02    35.50  36.28                                   ______________________________________                                        S           r         d        n      ν                                    ______________________________________                                         1          137.4739  1.500    1.84666                                                                              23.83                                    2          79.7675   1.000    1.0                                             3          78.3732   10.800   1.60300                                                                              65.42                                    4          -598.6823 0.100    1.0                                             5          75.4621   4.600    1.65160                                                                              58.44                                    6          146.9455  (D6)     1.0                                             7          224.7221  1.200    1.79450                                                                              45.40                                    8          31.6589   7.100    1.0                                             9          -378.7238 0.900    1.83500                                                                              42.97                                   10          41.4993   5.000    1.84666                                                                              23.83                                   11          ∞   (D11)    1.0                                            12          -47.6057  1.000    1.64850                                                                              53.03                                   13          54.3989   3.450    1.84666                                                                              23.83                                   14          290.6579  (D14)    1.0                                            15          ∞   0.600    1.0                                            16          70.4505   3.500    1.61800                                                                              63.39                                   17          907.3141  0.100    1.0                                            18          72.1525   7.800    1.49782                                                                              82.52                                   19          -50.1018  1.000    1.83400                                                                              37.35                                   20          -294.3438 (D21)    1.0                                            21          87.3203   3.600    1.74330                                                                              49.23                                   22          -209.5988 9.400    1.0                                            23          97.4086   10.100   1.49782                                                                              82.52                                   24          -41.5653  0.100    1.0                                            25          277.9666  2.300    1.80518                                                                              25.46                                   26          30.9389   7.250    1.0                                            27          72.6771   4.500    1.84666                                                                              23.83                                   28          -402.4976 4.200    1.0                                            29          -45.3072  1.000    1.83500                                                                              42.97                                   30          -73.7649  (Bf)     1.0                                            ______________________________________                                    

                                      TABLE 6b                                    __________________________________________________________________________    ASPHERIC COEFFICIENTS                                                         __________________________________________________________________________    S7  r = 10.010  C.sub.4  = 4.50670 × 10.sup.-7                                                      C.sub.6  = -1.04410 × 10.sup.-9             /// C.sub.8  = 1.67211 × 10.sup.-12                                                     C.sub.10  = -9.73390 × 10.sup.-16                       S21 r = 2.1883  C.sub.4  = -4.55797 × 10.sup.-6                                                     C.sub.6  = -2.02450 × 10.sup.-9             /// C.sub.8  = -4.43880 × 10.sup.-13                                                    C.sub.10  = -3.99852 × 10.sup.-15                       __________________________________________________________________________

                  TABLE 6c                                                        ______________________________________                                        VARIABLE SPACING WHEN VARYING POWER (ZOOMING)                                 FOCUSED ON OBJECT AT ∞                                                  Lens Position                                                                            a         b       c        d                                       ______________________________________                                        f          28.8000   70.0000 140.0000 194.0000                                D5         1.5000    25.3244 47.6863  55.7283                                 D11        6.6289    11.5568 12.5568  13.2952                                 D14        46.3869   18.7471 7.9119   1.7500                                  D21        25.5054   9.1361  3.5920   1.1000                                  Bf         38.0000   64.4385 74.1450  76.0749                                 f          28.8000   70.0000 140.0000 194.0000                                Δ3   1.9440    1.4647  1.9456   2.3918                                  ______________________________________                                    

                  TABLE 6d                                                        ______________________________________                                        DESIGN CONDITION VALUES                                                       ______________________________________                                                  f.sub.1  = 117.2135                                                           f.sub.2  = -42.1755                                                           f.sub.3  = -77.2760                                                           f.sub.4  = 88.1444                                                            f.sub.5  = 71.3964                                                            (8) (Ave. C) · f.sub.w  = 0.362                                      (9) D.sub.2 /f.sub.1 = 0.475                                                  (10) |r.sub.a |/D.sub.a  = 0.936                            (11) D.sub.5 /f.sub.w  = 0.326                                                (12) f.sub.1 /f.sub.t  = 0.604                                                (13) f.sub.3 /f.sub.2  = 1.832                                                (14) f.sub.4 /f.sub.5  = 1.235                                      ______________________________________                                    

In Working Examples 4-6 above, close-range focus can be performed bymoving any one of lens groups G1 through G6. Close-range focus can alsobe performed by moving first lens group G1 in the same manner as done inconventional four-group positive-negative-positive-positive zoom types.However, this approach is not suited for autofocusing since the lensdiameter of the focusing lens group tends to be large. In contrast, forthe zoom lens of the present invention, third lens group G3 or fourthlens group G4, arranged near of the center of the zoom lens, iswell-suited to be the focusing group, since the lens diameter of each ofthese groups is small.

Working Examples 7-10

Next, Working Examples 7-10 according to the present invention arediscussed. With reference to FIG. 10, a zoom lens 55 represents WorkingExamples 7-10 of the present invention and comprises, objectwise toimagewise, a first lens group G1 having a positive refractive power, asecond lens group G2 having a negative refractive power, a third lensgroup G3 having a negative refractive power, a fourth lens group G4having a positive refractive power, a fifth lens group G5 having apositive refractive power, and a sixth lens group G6 having a negativerefractive power. When zooming from the wide-angle state to thetelephoto state, at least one lens group among first lens group G1 andfourth lens group G4 moves axially, and second lens group G2 movesimagewise such that the air space between first lens group G1 and secondlens group G2 increases, the air space between second lens group G2 andthird lens group G3 increases, the air space between third lens group G3and fourth lens group G4 decreases, the air space between fourth lensgroup G4 and fifth lens group G5 decreases, and the air space betweenfifth lens group G5 and sixth lens group G6 changes. In addition,focusing from an infinite object to a close-range object is performed byaxially moving third lens group G3 objectwise.

Working Example 7

FIG. 11 shows the configuration of a zoom lens 60 according to WorkingExample 7 of the present invention. Zoom lens 60 has the same basicconfiguration as zoom lens 20 of FIG. 2 (Working Example 1).

Tables 7a-7d list the design values and design conditions for WorkingExample 7 of the present invention.

                  TABLE 7a                                                        ______________________________________                                        DESIGN TABLE                                                                  ______________________________________                                        f          28.80     70.00     140.00  194.00                                 FNO        2.90      2.90      2.90    2.90                                   2ω   75.65     33.15     16.95   12.22°                          Aperture Diameter                                                                        26.00     32.24     35.22   35.40                                  ______________________________________                                        S          r         d         n       ν                                   ______________________________________                                         1         161.8062  1.500     1.84666 23.83                                   2         76.7425   1.000                                                     3         76.9182   9.900     1.62041 60.35                                   4         -1133.1769                                                                              0.100                                                     5         70.9581   6.700     1.69350 53.31                                   6         253.4789  (d6 =                                                                         variable)                                                 7         1674.5951 1.200     1.81474 37.03                                   8         30.4350   7.750                                                     9         -200.8124 0.900     1.83500 42.97                                  10         41.4244   5.700     1.84666 23.83                                  11         -168.3388 (d11 =                                                                        variable)                                                12         -52.6800  1.000     1.67003 47.19                                  13         42.4871   3.800     1.84666 23.83                                  14         169.5940  (d14 =                                                                        variable)                                                15         ∞   0.700     Aperture                                                                      stop                                           16         61.5342   4.900     1.49782 82.52                                  17         -197.1872 0.100                                                    18         64.2715   5.000     1.49782 82.52                                  19         -193.6733 1.300                                                    20         -87.4033  0.800     1.83400 37.35                                  21         -6013.1438                                                                              (d21 =                                                                        variable)                                                22         66.9795   4.300     1.69680 55.48                                  23         -153.7929 9.200                                                    24         78.6865   9.100     1.49782 82.52                                  25         -41.1071  0.100                                                    26         -160.5423 1.000     1.82027 29.69                                  27         31.3268   6.450                                                    28         110.2877  4.700     1.71736 29.50                                  29         -70.1805  (d29 =                                                                        variable)                                                30         -38.0379  1.000     1.83500 42.97                                  31         -59.0360  (Bf)                                                     ______________________________________                                    

                                      TABLE 7b                                    __________________________________________________________________________    ASPHERIC COEFFICIENTS                                                         __________________________________________________________________________    S7  r = 1674.5951                                                                             κ = 5.5228                                                                          C.sub.4  = +1.23744 × 10.sup.-6             /// C.sub.6  = -7.80256 × 10.sup.-10                                                    C.sub.8  = +4.36329 × 10.sup.-13                                                    C.sub.10  = -9.00276 × 10.sup.-15           S22 r = 66.9795 κ = 2.3824                                                                          C.sub.4  = -5.00920 × 10.sup.-6             /// C.sub.6  = -2.89371 × 10.sup.-9                                                     C.sub.8  = +1.16663 × 10.sup.-12                                                    C.sub.10  = -9.00276 × 10.sup.-15           __________________________________________________________________________

                  TABLE 7c                                                        ______________________________________                                        VARIABLE SPACING WHEN VARYING POWER (ZOOMING)                                 FOCUSED ON OBJECT AT ∞                                                  Lens Position                                                                            a         b       c        d                                       ______________________________________                                        f          28.8000   70.0000 140.0007 194.0017                                d6         1.5000    22.4101 40.6790  47.9809                                 d11        4.6623    5.4954  5.4954   12.3558                                 d14        48.9055   21.7913 9.6248   1.7500                                  d21        28.7619   10.0340 2.4570   1.0000                                  d29        2.9672    4.3268  5.0384   4.3105                                  Bf         38.0002   60.7400 68.1438  69.4049                                 f          28.8000   70.0000 140.0007 194.0017                                Δ    1.8086    1.5162  2.0435   2.6518                                  ______________________________________                                    

                  TABLE 7d                                                        ______________________________________                                        DESIGN CONDITION VALUES                                                       ______________________________________                                               f.sub.1  = 100.5335 (1 = 0.009947)                                            f.sub.2  = -41.1088 (2 = -0.024326)                                           f.sub.3  = -73.2715 (3 = -0.013648)                                           f.sub.4  = 82.6660 (4 = 0.012097)                                             f.sub.5  = 57.2137 (5 = 0.017478)                                             f.sub.6  = -130.9127 (6 = -0.007639)                                          12.sub.t  = -0.00136                                                          (15) 12.sub.t  · f.sub.t  = -0.264                                   (16) |f.sub.3 |/(f.sub.w  · f.sub.t).sup           .1/2  = 0.980                                                                 (17) |MAX| · f.sub.t  =4.719                       (18) |2 + 3| · f.sub.w  = 1.094                    (19) |f.sub.3 |/f.sub.4  = 0.886                            (20) f.sub.1 /D.sub.12t  = 2.095                                       ______________________________________                                    

Working Example 8

FIG. 12 shows the configuration of the zoom lens 65 according to WorkingExample 8 of the present invention. Zoom lens 65 has the same basicconfiguration as zoom lens 50 of FIG. 9 (Working Example 6).

Tables 8a-8d list the design values and design conditions for WorkingExample 8 of the present invention.

                  TABLE 8a                                                        ______________________________________                                        DESIGN TABLE                                                                  ______________________________________                                        f          28.80     70.00     140.00  194.00                                 FNO        2.90      2.90      2.90    2.90                                   2ω   75.41     33.05     16.88   12.24°                          Aperture Diameter                                                                        25.60     31.48     33.84   35.34                                  ______________________________________                                        S          r         d         n       ν                                   ______________________________________                                         1         190.4150  1.500     1.84666 23.83                                   2         85.9379   1.000                                                     3         84.7483   9.800     1.62041 60.35                                   4         -423.7788 0.100                                                     5         69.0744   6.000     1.69680 55.48                                   6         171.7412  (d6 =                                                                         variable)                                                 7         393.1037  1.200     1.81474 37.03                                   8         31.5103   7.750                                                     9         -160.2839 0.900     1.83500 42.97                                  10         46.1305   5.350     1.84666 23.83                                  11         -163.1180 (d11 =                                                                        variable)                                                12         -51.0866  1.000     1.65844 50.84                                  13         44.3577   3.550     1.84666 23.83                                  14         167.0177  (d14 =                                                                        variable)                                                15         ∞   0.700     Aperture                                                                      stop                                           16         65.6168   4.100     1.49782 82.52                                  17         -371.0737 0.100                                                    18         66.7445   6.850     1.49782 82.52                                  19         -57.3842  1.000     1.83500 42.97                                  20         -904.8357 (d20 =                                                                        variable)                                                21         79.3307   3.350     1.74330 49.23                                  22         -203.2664 9.900                                                    23         86.2312   9.050     1.49782 82.52                                  24         -40.8025  0.100                                                    25         254.6695  1.000     1.80518 25.46                                  26         29.2625   7.050                                                    27         106.5051  3.400     1.84666 23.83                                  28         -162.0625 (d28 =                                                                        variable)                                                29         -46.2971  1.000     1.83500 42.97                                  30         -86.4862  (Bf)                                                     ______________________________________                                    

                                      TABLE 8b                                    __________________________________________________________________________    ASPHERIC COEFFICIENTS                                                         __________________________________________________________________________    S7  r = 393.1037                                                                              κ = 11.000                                                                          C.sub.4  = +7.64647 × 10.sup.-7             /// C.sub.6  = -5.49504 × 10.sup.-10                                                    C.sub.8  = +2.33357 × 10.sup.-13                                                    C.sub.10  = +1.04457 × 10.sup.-16           S21 r = 79.3307 κ = 2.2669                                                                          C.sub.4  = -5.18000 × 10.sup.-6             /// C.sub.6  = -2.51053 × 10.sup.-9                                                     C.sub.8  = -9.16437 × 10.sup.-13                                                    C.sub.10  = -5.29344 × 10.sup.-15           __________________________________________________________________________

                  TABLE 8c                                                        ______________________________________                                        VARIABLE SPACING WHEN VARYING POWER (ZOOMING)                                 FOCUSED ON OBJECT AT ∞                                                  Lens Position                                                                            a         b       c        d                                       ______________________________________                                        f          28.7997   69.9992 139.9987 193.9991                                d6         1.5000    23.8936 43.5476  49.4290                                 d11        4.7922    6.9315  8.4315   11.5431                                 d14        50.0388   21.8953 9.3535   1.7500                                  d20        31.0173   11.5624 4.5146   1.4000                                  d28        3.4633    4.3268  4.8912   4.1799                                  Bf         37.9997   59.9569 65.9685  70.9484                                 f          28.7997   69.9992 139.9987 193.9991                                Δ    1.9015    1.6078  2.2920   2.6695                                  ______________________________________                                    

                  TABLE 8d                                                        ______________________________________                                        DESIGN CONDITION VALUES                                                       ______________________________________                                               f.sub.1  = 104.4695 (1 = 0.009572)                                            f.sub.2  = -43.5791 (2 = -0.022947)                                           f.sub.3  = -72.4370 (3 = -0.013805)                                           f.sub.4  = 85.3736 (4 = 0.011713)                                             f.sub.5  = 55.8498 (5 = 0.017905)                                             f.sub.6  = -120.6842 (6 = -0.008286)                                          12.sub.t  = -0.001226                                                         (15) 12.sub.t  · f.sub.t  = -0.238                                   (16) |f.sub.3 |/f.sub.w  · f.sub.t).sup.           1/2  = 0.969                                                                  (17) |MAX| · f.sub.t  = 4.452                      (18)|2 + 3| · f.sub.w  = 1.058                     (19) |f.sub.3 |/f.sub.4  = 0.848                            (20) f.sub.1 /D.sub.12t  = 2.033                                       ______________________________________                                    

Working Example 9

FIG. 12 shows the configuration of a zoom lens 65 according to WorkingExample 9 of the present invention. Zoom lens 65 has the same basicconfiguration as zoom lens 25 of FIG. 4 (Working Example 2).

In Working Example 9, when zooming from the wide-angle state to thetelephoto state, first lens group G1 first moves imagewise and thenmoves objectwise, second lens group G2 and third lens group G3 moveimagewise, and fifth lens group G5 and sixth lens group G6 moveobjectwise such that the air space between first lens group G1 andsecond lens group G2 increases, the air space between second lens groupG2 and third lens group G3 increases, the air space between third lensgroup G3 and fourth lens group G4 decreases, the air space betweenfourth lens group G4 and fifth lens group G5 decreases, and the airspace between fifth lens group G5 and sixth lens group G6 firstincreases and then decreases. However, fourth lens group G4 is fixedalong the optical axis. In addition, an aperture stop AS is locatedadjacent fourth lens group G4 between third lens group G3 and fourthlens group G4. The aperture stop diameter increases when zooming fromthe wide-angle state to the telephoto state, although it is fixed alongthe optical axis together with fourth lens group G4.

Tables 9a-d lists the design values and design conditions for WorkingExample 9 of the present invention.

                  TABLE 9a                                                        ______________________________________                                        DESIGN TABLE                                                                  ______________________________________                                        f          28.80     70.00     140.00  194.00                                 FNO        2.90      2.90      2.90    2.90                                   2ω   75.59     33.05     16.92   12.25°                          Aperture Diameter                                                                        26.13     31.58     34.60   35.78                                  ______________________________________                                        S          r         d         n       ν                                   ______________________________________                                         1         176.1773  1.500     1.84666 23.83                                   2         81.5336   1.000                                                     3         80.8687   10.500    1.62041 60.35                                   4         -557.5412 0.100                                                     5         68.7958   6.450     1.69680 55.48                                   6         199.5057  (d6 =                                                                         variable)                                                 7         637.6892  1.200     1.81474 37.03                                   8         31.2514   7.950                                                     9         -144.5846 0.900     1.83500 42.97                                  10         48.1839   5.300     1.84666 23.83                                  11         -163.1988 (d11 =                                                                        variable)                                                12         -49.7238  1.000     1.62280 56.93                                  13         48.0796   3.300     1.84666 23.83                                  14         161.0550  (d14 =                                                                        variable)                                                15         ∞   0.700     Aperture                                                                      stop                                           16         68.3778   4.000     1.49782 82.52                                  17         -427.0582 0.100                                                    18         77.6111   6.950     1.49782 82.52                                  19         -52.1300  1.000     1.83500 42.97                                  20         -232.3430 (d20 =                                                                        variable)                                                21         61.6060   4.500     1.65160 58.44                                  22         -243.7490 7.700                                                    23         65.9685   12.000    1.49782 82.52                                  24         -42.5379  0.100                                                    25         -156.0129 1.000     1.80610 33.27                                  26         30.7964   5.000                                                    27         110.4314  4.550     1.74950 35.04                                  28         -72.1558  (d28 =                                                                        variable)                                                29         -38.2808  1.000     1.83500 42.97                                  30         -62.4862  (Bf)                                                     ______________________________________                                    

                                      TABLE 9b                                    __________________________________________________________________________    ASPHERIC COEFFICIENTS                                                         __________________________________________________________________________    S7  r = 637.6892                                                                              κ = 7.4504                                                                          C.sub.4  = +9.60240 × 10.sup.-7             /// C.sub.6  = -7.93770 × 10.sup.-10                                                    C.sub.8  = +7.86540 × 10.sup.-13                                                    C.sub.10  = -8.16590 × 10.sup.-16           S21 r = 61.6060 κ = 1.6361                                                                          C.sub.4  = -4.14690 × 10.sup.-6             /// C.sub.6  = -2.58840 × 10.sup.-9                                                     C.sub.8  = +5.30380 × 10.sup.-13                                                    C.sub.10  = -8.16590 × 10.sup.-15           __________________________________________________________________________

                  TABLE 9c                                                        ______________________________________                                        VARIABLE SPACING WHEN VARYING POWER (ZOOMING)                                 FOCUSED ON OBJECT AT ∞                                                  Lens Position                                                                            a         b       c        d                                       ______________________________________                                        f          28.8000   69.9995 139.9986 193.9967                                d6         1.5000    23.6870 40.9809  46.9308                                 d11        5.8385    7.3082  8.3922   11.7638                                 d14        50.3627   22.5670 9.4694   1.7500                                  d20        35.6896   13.1134 4.6612   1.4000                                  d28        3.0657    4.3377  4.8016   4.3599                                  Bf         37.9997   59.3036 67.2917  70.9942                                 f          28.8000   69.9995 139.9986 193.9967                                Δ    1.8781    1.6698  2.2143   2.6314                                  ______________________________________                                    

                  TABLE 9d                                                        ______________________________________                                        DESIGN CONDITION VALUES                                                       ______________________________________                                               f.sub.1  = 100.2638 (1 = 0.009974)                                            f.sub.2  = -40.5974 (2 = -0.024632)                                           f.sub.3  = -75.7326 (3 = -0.013204)                                           f.sub.4  = 82.8560 (4 = 0.012069)                                             f.sub.5  = 57.7304 (5 = 0.017322)                                             f.sub.6  = -120.6169 (6 = -0.008291)                                          12.sub.t  = -0.001563                                                         (15) 12.sub.t  · f.sub.t  = -0.303                                   (16) |f.sub.3 |/(f.sub.w  · f.sub.t).sup           .1/2  = 1.013                                                                 (17) |MAX| · f.sub.t  = 4.779                      (18) |2 + 3| · f.sub.w  = 1.090                    (19) |f.sub.3 |/f.sub.4  = 0.914                            (20) f.sub.1 /D.sub.12t  = 2.136                                       ______________________________________                                    

Working Example 10

FIG. 13 shows the configuration of a zoom lens 70 according to WorkingExample 10 of the present invention. Zoom lens 70 has the same basicconfiguration as zoom lens 65 of FIG. 12 (Working Example 9).

Tables 10a-d list the design values and design conditions for WorkingExample 10 of the present invention.

                  TABLE 10a                                                       ______________________________________                                        DESIGN TABLE                                                                  ______________________________________                                        f          28.80     70.00     140.00  194.00                                 FNO        2.90      2.90      2.90    2.90                                   2ω   75.48     33.05     16.91   12.25°                          Aperture Diameter                                                                        25.22     30.72     33.30   34.28                                  ______________________________________                                        S          r         d         n       ν                                   ______________________________________                                         1         156.9863  1.500     1.84666 23.83                                   2         81.6688   1.000                                                     3         79.9629   10.950    1.60300 65.42                                   4         -557.6591 0.100                                                     5         71.5456   5.950     1.69680 55.48                                   6         171.3790  (d6 =                                                                         variable)                                                 7         392.9948  1.200     1.79450 45.50                                   8         30.9447   7.100                                                     9         -1455.4522                                                                              0.900     1.83500 42.97                                  10         49.2595   4.400     1.84666 23.83                                  11         ∞   (d11 =                                                                        variable)                                                12         -48.0862  1.000     1.63854 55.48                                  13         44.6394   3.500     1.84666 23.83                                  14         155.2173  (d14 =                                                                        variable)                                                15         ∞   0.700     Aperture                                                                      stop                                           16         60.8264   4.500     1.49782 82.52                                  17         -272.3116 0.100                                                    18         65.4497   7.150     1.49782 82.52                                  19         -52.1048  1.000     1.83500 42.97                                  20         -1055.9683                                                                              (d20 =                                                                        variable)                                                21         71.2343   3.550     1.69680 55.48                                  22         -210.7443 9.100                                                    23         81.1307   9.000     1.49782 82.52                                  24         -38.8014  0.100                                                    25         -173.2366 1.000     1.71736 29.50                                  26         30.4812   5.900                                                    27         104.6971  4.100     1.75520 27.53                                  28         -91.7624  (d28 =                                                                        variable)                                                29         -37.8613  1.000     1.83500 42.97                                  30         -59.9719  (Bf)                                                     ______________________________________                                    

                                      TABLE 10b                                   __________________________________________________________________________    ASPHERIC COEFFICIENTS                                                         __________________________________________________________________________    S7  r = 392.9948                                                                              κ = 5.4783                                                                          C.sub.4  = +8.97960 × 10.sup.-7             /// C.sub.6  = -1.20390 × 10.sup.-9                                                     C.sub.8  = +1.97840 × 10.sup.-12                                                    C.sub.10  = -1.25910 × 10.sup.-16           S21 r = 71.2343 κ = 0.8801                                                                          C.sub.4  = -4.71710 × 10.sup.-6             /// C.sub.6  = -2.87190 × 10.sup.-9                                                     C.sub.8  = -9.24030 × 10.sup.-13                                                    C.sub.10  = -9.84880 × 10.sup.-15           __________________________________________________________________________

                  TABLE 10c                                                       ______________________________________                                        VARIABLE SPACING WHEN VARYING POWER (ZOOMING)                                 FOCUSED ON OBJECT AT ∞                                                  Lens Position                                                                            a         b       c        d                                       ______________________________________                                        f          28.8000   69.9996 139.9988 193.9984                                d6         1.5000    24.9218 44.0987  50.5007                                 d11        6.1351    8.2820  9.2820   12.4744                                 d14        47.5617   21.0223 9.0376   1.7500                                  d20        28.5968   10.7612 3.8044   1.1000                                  d28        3.5114    4.7114  5.0392   4.6703                                  f          28.8000   69.9996 139.9988 193.9984                                Δ    1.8016    1.5658  2.1628   2.6060                                  ______________________________________                                    

                  TABLE 10d                                                       ______________________________________                                        DESIGN CONDITION VALUES                                                       ______________________________________                                               f.sub.1  = 105.9365 (1 = 0.009440)                                            f.sub.2  = -41.6516 (2 = -0.024009)                                           f.sub.3  = -70.5885 (3 = -0.014167)                                           f.sub.4  = 79.2135 (4 = 0.012624)                                             f.sub.5  = 55.6390 (5 = 0.017973)                                             f.sub.6  = -125.5708 (6 = -0.007964)                                          12.sub.t  = -0.001407                                                         (15) 12.sub.t  · f.sub.t  = -0.273                                   (16) |f.sub.3 |/(f.sub.w  · f.sub.t).sup           .1/2  = 0.944                                                                 (17) |MAX| · f.sub.t  = 4.658                      (18)|2 + 3| · f.sub.w  = 1.099                     (19) |f.sub.3 |/f.sub.4  = 0.891                            (20) f.sub.1 /D.sub.12t  = 2.098                                       ______________________________________                                    

Working Examples 11-13

Next, Working Examples 11-13 according to the present invention arediscussed. With reference to FIG. 15a, zoom lens 80 represents WorkingExamples 11-13 and comprises, objectwise to imagewise, a first lensgroup G1 having a positive refractive power, a second lens group G2having a negative refractive power, a third lens group G3 having anegative refractive power, a fourth lens group G4 having a positiverefractive power, and a fifth lens group G5 having a positive refractivepower. When zooming from the wide-angle state to the telephoto state, atleast second lens group G2 and third lens group G3 move imagewise, andfifth lens group G5 moves objectwise such that the air space betweenfirst lens group G1 and second lens group G2 increases, the air spacebetween second lens group G2 and third lens group G3 increases, the airspace between third lens group G3 and fourth lens group G4 decreases,and the air space between fourth lens group G4 and fifth lens group G5decreases.

Working Example 11

FIG. 16 shows the configuration of a zoom lens 85 according to WorkingExample 11 of the present invention. Zoom lens 85 has the same basicconfiguration as zoom lens 75 of FIG. 14 (Working Example 10), exceptthat lens L22 is biconcave, and the objectwise surface of lens L41 issubstantially more planar (i.e., has a larger radius of curvature).

In Working Example 11, when zooming from the wide-angle state to thetelephoto state, second lens group G2 and third lens group G3 moveimagewise, and fourth lens group G4, fifth lens group G5, and sixth lensgroup G6 move objectwise such that the air space between first lensgroup G1 and second lens group G2 increases, the air space betweensecond lens group G2 and third lens group G3 increases, the air spacebetween third lens group G3 and fourth lens group G4 decreases, the airspace between fourth lens group G4 and fifth lens group G5 decreases,and the air space between fifth lens group G5 and sixth lens group G6changes. In addition, first lens group G1 is fixed along the opticalaxis. An aperture stop AS is located between third lens group G3 andfourth lens group G4, and moves together with fourth lens group G4. Theaperture stop diameter increases as the lens positional state changesfrom the wide-angle state to the telephoto state. Third lens group G3moves objectwise when focusing at close range.

Tables 11a-d list the design values and design conditions for WorkingExample 11 according to the present invention.

                  TABLE 11a                                                       ______________________________________                                        DESIGN TABLE                                                                  ______________________________________                                        f          28.80      70.00    140.00 194.00                                  FNO        2.88       2.88     2.88   2.88                                    2ω   76.38      33.30    17.08  12.34°                           Aperture Diameter                                                                        25.96      32.48    36.02  37.50                                   ______________________________________                                        S          r          d        n      ν                                    ______________________________________                                         1         138.3891   1.50     1.92286                                                                              20.88                                    2         75.4719    1.00     1.0                                             3         76.2996    11.30    1.59318                                                                              67.87                                    4         -818.7692  0.10     1.0                                             5         69.2981    7.10     1.74330                                                                              49.23                                    6         262.9790   (D6)     1.0                                             7         854.9644   1.20     1.81474                                                                              37.03                                    8         32.9128    7.60     1.0                                             9         -130.4347  0.90     1.80420                                                                              46.51                                   10         37.5987    5.35     1.92286                                                                              20.88                                   11         -1383.3263 (D11)    1.0                                            12         -50.5204   1.00     1.74330                                                                              49.23                                   13         93.7485    2.60     1.92286                                                                              20.88                                   14         894.4541   (D14)    1.0                                            15         ∞    0.70     1.0                                            16         2286.6278  3.20     1.62041                                                                              60.35                                   17         -88.1322   0.10     1.0                                            18         48.7611    9.90     1.49782                                                                              82.52                                   19         -51.1368   1.00     1.83400                                                                              37.35                                   20         -1041.6389 (D20)    1.0                                            21         82.4183    8.70     1.72000                                                                              50.35                                   22         -123.0703  3.80     1.0                                            23         69.0366    12.00    1.59318                                                                              67.87                                   24         -52.0987   0.10     1.0                                            25         -104.4301  1.85     1.83400                                                                              37.35                                   26         33.8911    (D26)    1.0                                            27         134.9880   4.75     1.71700                                                                              47.99                                   28         -77.2825   3.05     1.0                                            29         -45.9111   1.00     1.83500                                                                              42.97                                   30         -71.0022   (Bf)     1.0                                            ______________________________________                                    

                  TABLE 11b                                                       ______________________________________                                        ASPHERIC COEFFICIENTS                                                         ______________________________________                                        S7   r = -9.0000   C.sub.4  = +8.0005 × 10.sup.-7                                                        C.sub.6  = -4.4310 ×                                                    10.sup.-10                                   ///  C.sub.8  = +1.0014 × 10.sup.-12                                                       C.sub.10  = -6.3906 × 10.sup.-16                     S21  r = 1.4831    C.sub.4  = 2.9199 × 10.sup.-6                                                         C.sub.6  = -1.3176 ×                                                    10.sup.-9                                    ///  C.sub.8  = +3.8082 × 10.sup.-13                                                       C.sub.10  = -3.2978 × 10.sup.-15                     ______________________________________                                    

                  TABLE 11c                                                       ______________________________________                                        VARIABLE SPACING WHEN VARYING POWER (ZOOMING)                                 FOCUSED ON OBJECT AT ∞                                                  Lens Position                                                                            a         b       c        d                                       ______________________________________                                        f          28.7999   69.9996 139.9990 193.9985                                D6         1.2505    21.2320 35.1368  40.0476                                 D11        6.2635    10.4036 11.0036  14.3539                                 D14        49.8206   24.5159 10.0611  1.7500                                  D20        40.0191   10.1516 2.3489   1.6000                                  D26        4.2505    18.7866 11.0495  4.4293                                  Bf         37.9996   54.5639 70.1035  77.4725                                 f          28.8000   70.0000 140.0000 194.0000                                Δ3   1.8415    1.6188  1.9912   2.2570                                  ______________________________________                                    

                  TABLE 11d                                                       ______________________________________                                        DESIGN CONDITION VALUES                                                       ______________________________________                                                 f.sub.1  = 91.5599                                                            f.sub.2  = -37.8208                                                           f.sub.3  = -72.2560                                                           f.sub.5  = 139.0502                                                           f.sub.6  = 118.7562                                                           (21) f.sub.5 /f.sub.6  = 1.171                                                (22) D.sub.1 /(f.sub.1  - f.sub.w) = 0                                        (23) D.sub.2 /(f.sub.w  · f.sub.t).sup.1/2  = 0.519                  (24) D.sub.5 /(f.sub.w  · f.sub.t).sup.1/2  = 0.530                  (25) Δ2/(|f.sub.2 | + |f.sub.3               |) = 0.073                                                           (26) f.sub.1 /(f.sub.w  · f.sub.t).sup.1/2 = 1.225                   (27) M.sub.1 /M.sub.4  = 1.726                                       ______________________________________                                    

Working Example 12

FIG. 17 shows the configuration of a zoom lens 90 according to WorkingExample 12 of the present invention. Zoom lens 90 has the same basicconfiguration as zoom lens 85 of FIG. 16 (Working Example 11).

In Working Example 12, when zooming from the wide-angle state to thetelephoto state, first lens group G1 and fourth lens group G4 are fixedaxially, second lens group G2 and third lens group G3 move imagewisesuch that the air space between the second and third lens groupsincreases, fifth lens group G5 moves objectwise, and sixth lens group G6moves objectwise along a zoom trajectory that differs from fifth lensgroup G5. An aperture stop AS is located between third lens group G3 andfourth lens group G4. When zooming from the wide-angle state to thetelephoto state, the aperture stop diameter increases, although it isfixed with respect to the optical axis. Third lens group G3 movesobjectwise when focusing at close range.

Tables 12a-d list the design values and design conditions for WorkingExample 12 according to the present invention.

                  TABLE 12a                                                       ______________________________________                                        DESIGN TABLE                                                                  ______________________________________                                        f          28.80      70.00    140.00 194.00                                  FNO        2.88       2.88     2.88   2.88                                    2ω   76.40      33.31    17.08  12.33°                           Aperture Diameter                                                                        25.66      32.42    36.22  37.68                                   ______________________________________                                        S          r          d        n      ν                                    ______________________________________                                         1         144.3739   1.50     1.92286                                                                              20.88                                    2         76.4298    1.00     1.0                                             3         77.6169    11.25    1.59318                                                                              67.87                                    4         -758.9875  0.10     1.0                                             5         68.2287    7.20     1.74330                                                                              49.23                                    6         261.7709   (D6)     1.0                                             7         766.3932   1.20     1.81474                                                                              37.03                                    8         32.5037    7.70     1.0                                             9         -127.6918  0.90     1.80420                                                                              46.51                                   10         37.3748    5.50     1.92286                                                                              20.88                                   11         -723.9893  (D11)    1.0                                            12         -49.1806   1.00     1.74330                                                                              49.23                                   13         100.7266   2.55     1.92286                                                                              20.88                                   14         1613.0980  (D14)    1.0                                            15         ∞    0.70     1.0                                            16         937.6925   3.35     1.62041                                                                              60.35                                   17         -88.4816   0.10     1.0                                            18         50.2171    9.80     1.49782                                                                              82.52                                   19         -50.5734   1.00     1.83400                                                                              37.35                                   20         -4649.7697 (D20)    1.0                                            21         89.6907    5.70     1.72000                                                                              50.35                                   22         -115.3692  5.35     1.0                                            23         71.8816    12.00    1.59318                                                                              67.87                                   24         -50.3051   0.10     1.0                                            25         -104.4284  4.00     1.83400                                                                              37.35                                   26         34.2193    (D26)    1.0                                            27         127.2351   4.85     1.71700                                                                              47.99                                   28         -74.6444   3.00     1.0                                            29         -45.5316   1.00     1.83500                                                                              42.97                                   30         -72.1972   (Bf)     1.0                                            ______________________________________                                    

                  TABLE 12b                                                       ______________________________________                                        ASPHERIC COEFFICIENTS                                                         ______________________________________                                        S7   r = -9.0000   C.sub.4  = +8.4027 × 10.sup.-7                                                        C.sub.6  = -3.6910 ×                                                    10.sup.-10                                   ///  C.sub.8  = +8.1779 × 10.sup.-13                                                       C.sub.10  = -5.1312 × 10.sup.-16                     S21  r = 1.4956    C.sub.4  = -2.9113 × 10.sup.-6                                                        C.sub.6  = -1.4238 ×                                                    10.sup.-9                                    ///  C.sub.8  = +7.2661 × 10.sup.-13                                                       C.sub.10  = -3.7414 × 10.sup.-15                     ______________________________________                                    

                  TABLE 12c                                                       ______________________________________                                        VARIABLE SPACING WHEN VARYING POWER (ZOOMING)                                 FOCUSED ON OBJECT AT ∞                                                  Lens Position                                                                            a         b       c        d                                       ______________________________________                                        f          28.8047   69.9996 139.9990 193.9965                                D6         1.2000    21.3652 35.1808  40.1525                                 D11        6.3168    10.3779 10.9779  14.2604                                 D14        48.6945   24.4182 10.0532  1.7500                                  D20        39.3624   9.9075  2.1357   1.6000                                  D26        4.1192    17.6429 10.0228  3.4848                                  Bf         37.9980   53.9298 69.3209  76.3935                                 f          28.8000   70.0000 140.0000 194.0000                                Δ3   1.8393    1.6295  1.9870   2.2635                                  ______________________________________                                    

                  TABLE 12d                                                       ______________________________________                                        DESIGN CONDITION VALUES                                                       ______________________________________                                                 f.sub.1  = 91.7667                                                            f.sub.2  = -38.4566                                                           f.sub.3  = -71.9282                                                           f.sub.4  = 84.4339                                                            f.sub.5  = 128.7246                                                           f.sub.6  = 114.3856                                                           (21) f.sub.5 /f.sub.6  = 1.125                                                (22) D.sub.1 /(f.sub.1  - f.sub.w) = 0                                        (23) D.sub.2 /(f.sub.w  · f.sub.t).sup.1/2  = 0.521                  (24) D.sub.5 /(f.sub.w  · f.sub.t).sup.1/2  = 0.628                  (25) Δ2/(|f.sub.2 | + |f.sub.3               |) = 0.072                                                           (26) f.sub.1 /(f.sub.w  · f.sub.t).sup.1/2  = 1.228                  (27) M.sub.1 /M.sub.4  = 1.747                                       ______________________________________                                    

Working Example 13

FIG. 18 shows the configuration of a zoom lens as according to WorkingExample 13 of the present invention. Zoom lens 95 has the same generalconfiguration as zoom lens 90 of FIG. 17 (Working Example 12), exceptthat lens L41 is a positive meniscus lens having an objectwise concavesurface.

In Working Example 13, when zooming from the wide-angle state to thetelephoto state, first lens group G1 moves objectwise, second lens groupG2 and third lens group G3 move imagewise, and fifth lens group G5 andsixth lens group G6 move objectwise such that the air space betweenfirst lens group G1 and second lens group G2 increases, the air spacebetween second lens group G2 and third lens group G3 increases, the airspace between third lens group G3 and fourth lens group G4 decreases,the air space between fourth lens group G4 and fifth lens group G5decreases, and the air space between fifth lens group G5 and sixth lensgroup G6 changes. Also, when zooming from the wide-angle state to thetelephoto state, fourth lens group G4 is fixed with respect to theoptical axis. An aperture stop AS is located between third lens group G3and fourth lens group G4. When zooming from the wide-angle state to thetelephoto state, the aperture stop diameter increases, although it isfixed with respect to the optical axis. Third lens group G3 movesobjectwise when focusing at close range.

Tables 13a-d below list the design values and design conditions forWorking Example 13 according to the present invention.

                  TABLE 13a                                                       ______________________________________                                        DESIGN TABLE                                                                  ______________________________________                                        f          28.80      70.00    140.00 194.00                                  FNO        2.88       2.88     2.88   2.88                                    2ω   76.23      33.37    17.02  12.31°                           Aperture Diameter                                                                        25.26      32.12    35.98  37.48                                   ______________________________________                                        S          r          d        n      ν                                    ______________________________________                                         1         198.2709   1.50     1.84666                                                                              23.83                                    2         89.8483    1.00     1.0                                             3         88.6175    10.80    1.60300                                                                              65.42                                    4         -340.0238  0.10     1.0                                             5         73.7095    5.20     1.71300                                                                              53.93                                    6         153.6693   (D6)     1.0                                             7         277.6968   1.20     1.79668                                                                              45.37                                    8         34.1275    7.40     1.0                                             9         -162.7658  0.90     1.77250                                                                              49.61                                   10         38.8612    5.30     1.84666                                                                              23.83                                   11         ∞    (D11)    1.0                                            12         -46.0766   1.00     1.65160                                                                              58.44                                   13         90.6302    2.80     1.84666                                                                              23.83                                   14         1186.5200  (D14)    1.0                                            15         ∞    0.72     1.0                                            16         -321.4315  2.25     1.59318                                                                              67.87                                   17         -98.7415   0.10     1.0                                            18         61.1386    9.20     1.59318                                                                              67.87                                   19         -42.5094   1.00     1.83400                                                                              37.35                                   20         -296.1661  (D20)    1.0                                            21         85.1944    12.15    1.71300                                                                              53.93                                   22         -112.0244  2.60     1.0                                            23         66.9878    12.00    1.49782                                                                              82.52                                   24         -47.2487   0.10     1.0                                            25         -116.3858  6.30     1.83400                                                                              37.35                                   26         34.2324    (D26)    1.0                                            27         125.4407   4.95     1.70154                                                                              41.15                                   28         -72.2240   3.10     1.0                                            29         -43.6389   1.00     1.83500                                                                              42.97                                   30         -64.4054   (Bf)     1.0                                            ______________________________________                                    

                  TABLE 13b                                                       ______________________________________                                        ASPHERIC COEFFICIENTS                                                         ______________________________________                                        S7   r = -7.8623   C.sub.4  = +4.6110 × 10.sup.-7                                                        C.sub.6  = -4.1866 ×                                                    10.sup.-10                                   ///  C.sub.8  = +1.2514 × 10.sup.-12                                                       C.sub.10  = -9.7310 × 10.sup.-16                     S21  r = 2.8770    C.sub.4  = -3.2424 × 10.sup.-6                                                        C.sub.6  = -1.7925 ×                                                    10.sup.-9                                    ///  C.sub.8  = +1.0193 × 10.sup.-12                                                       C.sub.10  = -4.6187 × 10.sup.-15                     ______________________________________                                    

                  TABLE 13c                                                       ______________________________________                                        VARIABLE SPACING WHEN VARYING POWER (ZOOMING)                                 FOCUSED ON OBJECT AT ∞                                                  Lens Position                                                                            a         b       c        d                                       ______________________________________                                        f          28.8000   70.0000 139.9985 193.9971                                D6         1.4667    26.7287 47.6556  55.0299                                 D11        8.3049    8.3049  11.1757  13.9284                                 D14        46.0314   21.9738 8.9055   1.7500                                  D20        39.5925   11.1567 3.4583   1.6000                                  D26        3.8441    12.4549 6.7700   3.6349                                  Bf         38.0000   57.8242 71.2070  76.2000                                 f          28.8000   70.0000 140.0000 194.0000                                Δ3   1.9265    1.6452  2.0334   2.3486                                  ______________________________________                                    

                  TABLE 13d                                                       ______________________________________                                        DESIGN CONDITION VALUES                                                       ______________________________________                                                 f.sub.1  = 116.04455                                                          f.sub.2  = -42.25306                                                          f.sub.3  = -78.71789                                                          f.sub.4  = 88.79801                                                           f.sub.5  = 129.65876                                                          f.sub.6  = 106.51749                                                          (21) f.sub.5 /f.sub.6  = 1.217                                                (22) D.sub.1 /(f.sub.t  - f.sub.w) = 0.090                                    (23) D.sub.2 /(f.sub.w  · f.sub.t).sup.1/2  = 0.517                  (24) D.sub.5 /(f.sub.w  · f.sub.t).sup.1/2  = 0.508                  (25) Δ2/(|f.sub.2 | + |f.sub.3               |) = 0.046                                                           (26) f.sub.1 /(f.sub.w  · f.sub.t  ).sup.1/2  =             ______________________________________                                                 1.552                                                            

The zoom lenses of Working Examples 11, 12 and 13 of the presentinvention as described above, have an aperture ratio on the order of FNONo. 2.8, a field angle in the wide-angle state exceeding 75°, and a zoomratio on the order of 7×. In addition, a reduction in the lens diameterand a reduction in the overall length of the lens in the telephoto statewere simultaneously achieved by the appropriate use of asphericalsurfaces. An increased zoom ratio and aperture size, or increasedcompactness may be attained by the further use of aspherical surfaces.Also, in Working Example 11, when zooming from the wide-angle state tothe telephoto state, first lens group G1 is fixed at a position alongthe optical axis. However, this first lens group may also be moved inthe range consistent with design condition (2).

Working Examples 14-16

Next, Working Examples 14-16 according to the present invention arediscussed. With reference to FIG. 19, zoom lens 100 represents WorkingExamples 14-16 and comprises, objectwise to imagewise, a first lensgroup G1 having positive refractive power, a second lens group G2 havingnegative refractive power, a third lens group G3 having negativerefractive power, a fourth lens group G4 having a positive refractivepower, and a fifth lens group G5 having positive refractive power.Accordingly, when zooming from the wide-angle state to the telephotostate, at least second lens group G2 and third lens group G3 moveimagewise, and fifth lens group G5 moves objectwise so that the airspace between first lens group G1 and second lens group G2 increases,the air space between second lens group G2 and third lens group G3increases, the air space between third lens group G3 and fourth lensgroup G4 decreases, and the air space between fourth lens group G4 andfifth lens group G5 decreases.

Working Example 14

FIG. 20 shows the lens configuration of a zoom lens 105 according toWorking Example 14 of the present invention. Lens groups G1-G4 of zoomlens 105 have the same basic configuration as lens groups G1-G4 of zoomlens 45 of FIG. 8 (Working Example 5). Fifth lens group G5 comprises apositive biconvex lens L51, a biconvex lens L52, a biconcave lens L53and a biconvex lens L54. An aperture stop AS is located between thirdlens group G3 and fourth lens group G4, and moves together with fourthlens group G4. The aperture stop diameter increases as the lenspositional state changes from the wide-angle state to the telephotostate. In addition, third lens group G3 moves objectwise when focusingat close range.

Tables 14a-d list the design values and design conditions for WorkingExample 14 according to the present invention.

                  TABLE 14a                                                       ______________________________________                                        DESIGN TABLE                                                                  ______________________________________                                        f          28.80      70.00    140.00 194.00                                  FNO        2.90       2.90     2.90   2.90                                    2ω   76.19      33.30    17.03  12.34°                           Aperture Diameter                                                                        25.02      31.46    35.32  35.98                                   ______________________________________                                        S          r          d        n      ν                                    ______________________________________                                         1         132.3062   1.500    1.84666                                                                              23.83                                    2         79.2121    1.000    1.0                                             3         78.3091    11.200   1.60309                                                                              65.42                                    4         -532.8922  0.100    1.0                                             5         73.5167    4.300    1.65160                                                                              58.44                                    6         126.0337   (D6)     1.0                                             7         193.2957   1.200    1.77250                                                                              49.61                                    8         30.4799    7.950    1.0                                             9         -225.6733  0.900    1.77250                                                                              49.61                                   10         58.5416    3.900    1.84666                                                                              23.83                                   11         ∞    (D11)    1.0                                            12         -44.9319   1.000    1.62280                                                                              56.93                                   13         52.8818    3.250    1.84666                                                                              23.83                                   14         227.8615   (D14)    1.0                                            15         ∞    0.700    1.0                                            16         88.1418    3.300    1.59319                                                                              67.87                                   17         -578.8843  0.100    1.0                                            18         49.4409    8.650    1.49782                                                                              82.52                                   19         -52.6791   1.000    1.83500                                                                              42.97                                   20         1988.2645  (D20)    1.0                                            21         406.5779   4.000    1.69680                                                                              45.48                                   22         -92.0325   0.100    1.0                                            23         67.9050    13.000   1.65160                                                                              58.44                                   24         -50.3510   0.100    1.0                                            25         -76.7669   7.000    1.83400                                                                              37.35                                   26         43.6883    7.000    1.0                                            27         930.6501   4.650    1.62041                                                                              60.35                                   28         -56.3613   (Bf)     1.0                                            ______________________________________                                    

                                      TABLE 14b                                   __________________________________________________________________________    ASPHERIC COEFFICIENTS                                                         __________________________________________________________________________    S7  r = 7.3794  C.sub.4  = +3.85273 × 10.sup.-7                                                     C.sub.6  = -1.17922 × 10.sup.-9             /// C.sub.8  = +2.51899 × 10.sup.-12                                                    C.sub.10  = -1.71315 × 10.sup.-15                       S21 r = 11.0000 C.sub.4  = -4.22179 × 10.sup.-6                                                     C.sub.6  = -7.52773 × 10.sup.-10            /// C.sub.8  = -5.36928 × 10.sup.-13                                                    C.sub.10  = -2.80474 × 10.sup.-15                       __________________________________________________________________________

                  TABLE 14c                                                       ______________________________________                                        VARIABLE SPACING WHEN VARYING POWER (ZOOMING)                                 FOCUSED ON OBJECT AT ∞                                                  Lens Position                                                                            a         b       c        d                                       ______________________________________                                        f          28.8000   70.0000 140.0007 194.0017                                D5         1.5000    27.0469 48.7470  52.2784                                 D11        7.5535    10.8417 11.4417  12.0417                                 D14        44.9410   18.4841 7.5263   1.7500                                  D21        21.9616   8.7679  3.8265   1.7958                                  Bf         50.2372   76.9262 89.3996  91.2335                                 f          28.8000   70.0000 140.0000 194.0000                                Δ3   1.7981    1.4367  1.8116   2.2466                                  ______________________________________                                    

                  TABLE 14d                                                       ______________________________________                                        DESIGN CONDITION VALUES                                                       ______________________________________                                                f.sub.1  = 119.9234                                                           f.sub.2  = -42.0547                                                           f.sub.3  = -74.6172                                                           f.sub.4  = 85.9153                                                            f.sub.5  = 70.2983                                                            f.sub.b  = -66.0953                                                           f.sub.12t  = -423.364                                                         (28) (r.sub.1  + r.sub.2)/(r.sub.1  - r.sub.2) = 0.886                        (29) |f.sub.b |/f.sub.5  = 0.940                            (30) (f.sub.4  - f.sub.5)/(f.sub.4  + f.sub.5) = 0.100                        (31) f.sub.1 /|f.sub.2 | = 2.852                            (32) (f.sub.2  - f.sub.3)/(f.sub.2  + f.sub.3) = -0.279                       (33) f.sub.t /|f.sub.12t | = 0.458                  ______________________________________                                    

Working Example 15

FIG. 21 shows the configuration of a zoom lens 110 according to WorkingExample 15 of the present invention. Zoom lens 110 has the same basicconfiguration as zoom lens 105 of FIG. 19 (Working Example 14). Anaperture stop AS is located between third lens group G3 and fourth lensgroup G4, and moves together with fourth lens group G4. The aperturestop diameter increases as the lens positional state changes from thewide-angle state to the telephoto state. Third lens group G3 movesobjectwise when focusing at close range.

Tables 15a-d list the design values and design conditions for WorkingExample 15 of the present invention.

                  TABLE 15a                                                       ______________________________________                                        DESIGN TABLE                                                                  ______________________________________                                        f          28.80      70.00    140.00 194.00                                  FNO        2.90       2.90     2.90   2.90                                    2ω   76.27      33.30    17.03  12.34°                           Aperture Diameter                                                                        24.98      31.28    35.18  35.86                                   ______________________________________                                        S          r          d        n      ν                                    ______________________________________                                         1         117.1024   1.500    1.92286                                                                              20.88                                    2         80.6231    1.000    1.0                                             3         80.2776    10.580   1.60300                                                                              65.42                                    4         -717.9301  0.100    1.0                                             5         76.6585    4.400    1.65160                                                                              58.44                                    6         131.1840   (D6)     1.0                                             7         188.4345   1.200    1.80420                                                                              46.51                                    8         30.4799    7.920    1.0                                             9         -249.2295  0.900    1.77250                                                                              49.61                                   10         53.8578    3.940    1.84666                                                                              23.83                                   11         ∞    (D11)    1.0                                            12         -44.0313   1.000    1.62280                                                                              56.93                                   13         51.8050    3.280    1.84666                                                                              23.83                                   14         221.8299   (D14)    1.0                                            15         ∞    0.700    1.0                                            16         77.7674    3.450    1.59319                                                                              67.87                                   17         -1048.4714 0.100    1.0                                            18         53.4900    8.330    1.49782                                                                              82.52                                   19         -51.9829   1.000    1.83500                                                                              42.97                                   20         ∞    (D20)    1.0                                            21         303.6197   3.000    1.75500                                                                              52.32                                   22         -98.6602   3.600    1.0                                            23         133.3430   13.000   1.60300                                                                              65.47                                   24         -44.7587   0.100    1.0                                            25         -117.7427  7.000    1.80610                                                                              33.27                                   26         46.8016    6.470    1.0                                            27         349.8673   3.560    1.80420                                                                              46.51                                   28         -96.9906   (Bf)     1.0                                            ______________________________________                                    

                                      TABLE 15b                                   __________________________________________________________________________    ASPHERIC COEFFICIENTS                                                         __________________________________________________________________________    S7  r = -0.2776 C.sub.4  = +5.03090 × 10.sup.-7                                                     C.sub.6  = -9.02122 × 10.sup.-10            /// C.sub.8  = +1.84810 × 10.sup.-12                                                    C.sub.10  = -1.26710 × 10.sup.-15                       S21 r = 1.4967  C.sub.4  = -4.76220 × 10.sup.-6                                                     C.sub.6  = -7.54770 × 10.sup.-10            /// C.sub.8  = -1.39350 × 10.sup.-12                                                    C.sub.10  = -5.68570 × 10.sup.-16                       __________________________________________________________________________

                  TABLE 15c                                                       ______________________________________                                        VARIABLE SPACING WHEN VARYING POWER (ZOOMING)                                 FOCUSED ON OBJECT AT ∞                                                  Lens Position                                                                            a         b       c        d                                       ______________________________________                                        f          28.8002   70.0004 140.0008 194.0009                                D5         1.5000    27.0603 48.2785  56.6649                                 D11        8.2306    10.6283 11.2283  11.8283                                 D14        43.4664   18.2124 7.4043   1.7500                                  D21        21.1458   8.5565  3.6850   1.7000                                  Bf         50.8695   77.2317 90.0235  91.9270                                 f          28.8002   70.0004 140.0008 194.0009                                Δ3   1.7158    1.4068  1.7659   2.1887                                  ______________________________________                                    

                  TABLE 15d                                                       ______________________________________                                        DESIGN CONDITION VALUES                                                       ______________________________________                                                f.sub.1  = 118.8613                                                           f.sub.2  = -41.5933                                                           f.sub.3  = -72.9824                                                           f.sub.4  = 86.3188                                                            f.sub.5  = 69.5681                                                            f.sub.b  = -86.0682                                                           f.sub.12t  = -424.898                                                         (28) (r.sub.1  + r.sub.2)/(r.sub.1  - r.sub.2) = 0.566                        (29) |f.sub.b |/f.sub.5  = 1.237                            (30) (f.sub.4  - f.sub.5)/(f.sub.4  + f.sub.5) = 0.107                        (31) f.sub.1 /|f.sub.2 | = 2.856                            (32) (f.sub.2  - f.sub.3)/(f.sub.2  + f.sub.3) = -0.274                       (33) f.sub.t /|f.sub.12t | = 0.457                  ______________________________________                                    

Working Example 16

FIG. 21 shows the configuration of a zoom lens 115 according to WorkingExample 16 of the present invention. Zoom lens 115 has the same basicconfiguration as zoom lens 110 of FIG. 20 (Working Example 15). Anaperture stop AS is located between third lens group G3 and fourth lensgroup G4 and moves together with fourth lens group G4. The aperture stopdiameter increases as the lens positional state from the wide-anglestate to the telephoto state. Third lens group G3 moves objectwise whenfocusing at close range.

Tables 16a-d list the design values and design conditions for WorkingExample 16 of the present invention.

                  TABLE 16a                                                       ______________________________________                                        DESIGN TABLE                                                                  ______________________________________                                        f          28.80      70.00    140.00 194.00                                  FNO        2.90       2.90     2.90   2.90                                    2ω   76.25      33.30    17.03  12.34°                           Aperture Diameter                                                                        25.62      32.20    26.52  32.20                                   ______________________________________                                        S          r          d        n      ν                                    ______________________________________                                         1         115.8022   1.500    1.92286                                                                              20.88                                    2         79.4173    1.000    1.0                                             3         79.0424    10.730   1.60300                                                                              65.42                                    4         -701.5145  0.100    1.0                                             5         76.7245    4.330    1.65160                                                                              58.44                                    6         127.3222   (D6)     1.0                                             7         182.6349   1.200    1.80420                                                                              46.51                                    8         30.2450    8.060    1.0                                             9         -219.8733  0.900    1.77250                                                                              49.61                                   10         46.8071    4.360    1.84666                                                                              23.83                                   11         ∞    (D11)    1.0                                            12         -42.8771   1.000    1.62280                                                                              56.93                                   13         54.7586    6.030    1.84666                                                                              23.83                                   14         268.8082   (D14)    1.0                                            15         ∞    0.700    1.0                                            16         94.9355    3.940    1.49782                                                                              82.52                                   17         -208.7690  0.100    1.0                                            18         50.5793    9.220    1.49782                                                                              82.52                                   19         -55.6780   1.000    1.83400                                                                              37.35                                   20         3712.9134  (D20)    1.0                                            21         240.6326   7.850    1.74330                                                                              49.23                                   22         -93.7463   4.410    1.0                                            23         118.8725   9.580    1.48749                                                                              70.45                                   24         -42.3887   0.100    1.0                                            25         -158.9909  7.000    1.83400                                                                              37.35                                   26         46.9155    4.300    1.0                                            27         269.8997   3.500    1.80420                                                                              46.51                                   28         -113.1850  (Bf)     1.0                                            ______________________________________                                    

                                      TABLE 16b                                   __________________________________________________________________________    ASPHERIC COEFFICIENTS                                                         __________________________________________________________________________    S7  r = -4.2993 C.sub.4  = +5.73421 × 10.sup.-7                                                     C.sub.6  = -9.28161 × 10.sup.-10            /// C.sub.8  = +1.88381 × 10.sup.-12                                                    C.sub.10  = -1.29468 × 10.sup.-15                       S21 r = 8.7601  C.sub.4  = -4.85424 × 10.sup.-6                                                     C.sub.6  = -1.26065 × 10.sup.-9             /// C.sub.8  = -2.95632 × 10.sup.-13                                                    C.sub.10  = -2.74874 × 10.sup.-15                       __________________________________________________________________________

                  TABLE 16c                                                       ______________________________________                                        VARIABLE SPACING WHEN VARYING POWER (ZOOMING)                                 FOCUSED ON OBJECT AT ∞                                                  Lens Position                                                                            a         b       c        d                                       ______________________________________                                        f          28.7999   69.9997 139.9991 193.9984                                D5         1.5000    27.1463 48.4908  56.9003                                 D11        8.2407    10.0787 10.6787  11.2787                                 D14        43.0788   17.8880 7.2001   1.7500                                  D21        22.6609   8.8857  3.7274   1.7000                                  Bf         52.6277   80.2031 94.4433  97.4598                                 f          28.7999   69.9997 139.9991 193.9984                                Δ3   1.6616    1.3566  1.6640   2.0157                                  ______________________________________                                    

                  TABLE 16d                                                       ______________________________________                                        DESIGN CONDITION VALUES                                                       ______________________________________                                                 f.sub.1  = 120.2915                                                           f.sub.2  = -41.0605                                                           f.sub.3  = -73.0708                                                           f.sub.4  = 84.8082                                                            f.sub.5  = 72.6558                                                            f.sub.b  = -84.7356                                                           f.sub.12t  = -374.623                                                         (28) (r.sub.1  + r.sub.2)/(r.sub.1  - r.sub.2) = 0.409                        (29) |f.sub.b |/f.sub.5  = 1.166                            (30) (f.sub.4  - f.sub.5  )/(f.sub.4  + f.sub.5) = 0.077                      (31) f.sub.1 /|f.sub.2 | = 2.930                            (32) (f.sub.2  - f.sub.3  )/(f.sub.2  + f.sub.3) = -0.280                     (33) f.sub.t /|f.sub.12t | = 0.518                 ______________________________________                                    

According to the various Working Examples of the present invention asset forth above, a zoom lens was achieved having an aperture ratio onthe order of FNO 2.8, a field angle in the wide-angle state exceeding75°, and a zoom ratio on the order of 7×. In addition, in each WorkingExample, a reduction in the lens diameter and a reduction in the overalllength of the lens in the telephoto state was simultaneously achieved bythe appropriate introduction of aspherical surfaces. The aperture size,zoom ratio, and zoom lens compactness could be further increased by thefurther introduction of aspherical surfaces.

In Working Examples 1 through 16 of the present invention, set forthabove, aberrations are substantially and satisfactorily corrected at abrightness of FNO 2.8 in each focal length state from the maximumwide-angle state (f=28.8 mm) to the maximum telephoto state (f=194.0mm), and aberrations are satisfactorily corrected in the image planewithin a range up to an image height of 21.6 mm. Furthermore, in WorkingExamples 4-16, correction of aberrations is satisfactorily achieved at abrightness of imagewise numerical aperture NA=0.17 even in a close-rangefocus state wherein the lateral magnification is approximately -1/30,and correction of aberrations is satisfactorily achieved in the imageplane within a range up to an image height of 21.6 mm.

In addition, in the Working Examples set forth above, at least oneentire lens group among the plurality of lens groups G1 to G6 comprisingthe zoom lens could also be non-axially provided, or certain sub-lensgroups among at least one lens group among the plurality of lens groupsG1 to G5 could also be non-axially movably provided. Also, a blur (i.e.,anti-vibration) detection system, as discussed above, can be built intothe zoom lens. Consequently, image blurring can be corrected bydetecting vibration of the zoom lens by the blur detection system, andshifting the image by shifting the eccentric lens group(s) by the drivemeans such that the detected blurring is corrected. Based on such aconfiguration, it is possible to prevent failures due to image blurringcaused by hand vibration and the like, which tends to occur with highzoom ratio zoom lenses.

In each of the Working Examples described above, the radius ofcurvature, surface spacing and focal length are in units of mm, and eachnumerical working example has an image circle ideally suited toLeica-sized (Leica format: 24×36 mm) film. However, the presentinvention is not limited only to the use of Leica-sized film. Forexample, it is also suited to use in advanced photo systems (APS: 18×24mm) film, and to image pickup devices like CCDs.

The abovementioned preferred embodiments for carrying out the presentinvention are strictly intended to clarify the technical details of thepresent invention; therefore, the present invention is not limited tothe abovementioned preferred embodiments for carrying out the presentinvention, nor shall it be interpreted in the narrow sense.Alternatives, modifications and equivalents can be constructed withinthe scope of the present invention as defined in the appended claims.

What is claimed is:
 1. A zoom lens capable of forming an image of anobject and zooming between a maximum wide-angle state and a maximumtelephoto state, the zoom lens comprising objectwise to imagewise:a) afirst lens group having overall positive refractive power; b) a secondlens group having one or more surfaces each arranged along an opticalaxis and each with a paraxial curvature, said second lens group havingoverall negative refractive power and separated from said first lensgroup by a first air space; c) a third lens group having overallnegative refractive power and separated from said second lens group by asecond air space; d) a fourth lens group having overall positiverefractive power and separated from said third lens group by a third airspace; e) a fifth lens group having positive refractive power andseparated from said fourth lens group by a fourth air space; f) whereinthe zoom lens is designed such that when zooming from the maximumwide-angle state to the maximum telephoto state, at least said secondlens group moves imagewise and at least one of said first lens group andsaid fourth lens group moves so as to increase said first air space,increase said second air space, decrease said third air space, anddecrease said fourth air space; and g) wherein the following designcondition is satisfied:

    0.1<(Ave. C)·f.sub.w <0.6

wherein, Ave. C is the average value of the absolute value of saidparaxial curvature of each of said one or more lens surfaces comprisingsaid second lens group, and f_(w) is the focal length of the entire zoomlens in the maximum wide-angle state.
 2. The zoom lens according toclaim 1, satisfying the condition

    0.45<D.sub.2 /f.sub.1 <0.55

wherein D₂ is the axial extent of said first air space when the zoomlens is in the maximum telephoto state, and f₁ is the focal length ofsaid first lens group.
 3. A zoom lens according to claim 2, wherein saidsecond lens group comprises, from objectwise to imagewise, a negativelens having an imagewise concave surface, and a cemented lens comprisinga biconcave lens and a positive lens.
 4. A zoom lens according to claim3, further including an aperture stop located adjacent said fourth lensgroup.
 5. A zoom lens according to claim 4, wherein:a) said aperturestop is located between said third lens group and said fourth lensgroup; b) said third lens group includes a negative lens arranged mostobjectwise in said third lens group, and having a concave surface facingtoward the object; and c) the following condition is satisfied:

    0.7<|r.sub.a |/D.sub.a <1.3

wherein, r_(a) is the radius of curvature of said objectwise concavesurface of said negative lens, and D_(a) is the axial distance betweensaid objectwise concave surface of said negative lens and said aperturestop when the zoom lens is in the maximum wide-angle state.
 6. The zoomlens according to claim 1, wherein:a) said fifth lens group includes afirst subgroup having positive refractive power, and a second subgrouparranged imagewise of said first subgroup, and b) the followingcondition is satisfied:

    0.15<D.sub.5 /f.sub.w <0.45

wherein, D₅ is the axial extent of the air space between said first andsecond subgroups.
 7. A zoom lens according to claim 6, wherein saidfifth lens group includes a lens surface that is aspherical.
 8. A zoomlens according to claim 7, wherein an aperture stop is located betweensaid third lens group and said fourth lens group.
 9. A zoom lens capableof forming an image of an object and zooming between a maximumwide-angle state and a maximum telephoto state, the zoom lens comprisingobjectwise to imagewise:a) a first lens group having overall positiverefractive power; b) a second lens group having overall negativerefractive power and separated from said first lens group by a first airspace; c) a third lens group having overall negative refractive powerand separated from said second lens group by a second air space; d) afourth lens group having overall positive refractive power and separatedfrom said third lens group by a third air space; e) a fifth lens grouphaving positive refractive power and separated from said fourth lensgroup by a fourth air space; f) wherein the zoom lens is designed suchthat when zooming from the maximum wide-angle state to the maximumtelephoto state, at least said second lens group moves imagewise and atleast one of said first lens group and said fourth lens group moves soas to increase said first and second air spaces and decrease said thirdand fourth air spaces; and g) wherein the following condition issatisfied:

    0.4<f.sub.1 /f.sub.t <0.7

wherein, f_(t) is the focal length of the zoom lens in the maximumtelephoto state, and f₁ is the focal length of said first lens group.10. A zoom lens according to claim 9 satisfying at least one of theconditions:

    1.2<f.sub.3 /f.sub.2 <2.2

    0.7<f.sub.4 /f.sub.5 <1.5

wherein f₂ is the focal length of said second lens group, f₃ is thefocal length of said third lens group, f₄ is the focal length of saidfourth lens group, and f₅ is the focal length of said fifth lens group.11. A zoom lens capable of forming an image of an object and zoomingbetween a maximum wide-angle state and a maximum telephoto state, thezoom lens comprising objectwise to imagewise:a) a first lens grouphaving overall positive refractive power; b) a second lens group havingoverall negative refractive power and separated from said first lensgroup by a first air space; c) a third lens group having overallnegative refractive power and separated from said second lens group by asecond air space; d) a fourth lens group having overall positiverefractive power and separated from said third lens group by a third airspace; e) a fifth lens group having positive refractive power andseparated from said fourth lens group by a fourth air space; f) whereinthe zoom lens is designed such that when zooming from the maximumwide-angle state to the maximum telephoto state, at least said secondlens group moves imagewise and at least one of said first lens group andsaid fourth lens group moves so as to increase said first and second airspaces and decrease said third and fourth air spaces; g) an aperturestop is located between said first lens group and said fifth lens group;h) said fifth lens group comprising objectwise to imagewise, a positivelens subgroup which includes at least one positive lens component, and anegative lens subgroup which includes a negative lens component and apositive lens component arranged imagewise of said negative lenscomponent; and i) the following condition is satisfied:

    0.15<(r.sub.1 +r.sub.2)/(r.sub.1 -r.sub.2)<1.2

wherein, r₁ is the radius of curvature of the most objectwise surface ofsaid positive lens component in said negative lens subgroup, and r₂ isthe radius of curvature of the most imagewise surface of said positivelens component in said negative lens subgroup.
 12. A zoom lens accordingclaim 11, wherein at least one lens group arranged imagewise of saidfirst lens group is designed so as to move when focusing.
 13. A zoomlens according to claim 12, wherein only said third lens group isdesigned so as to move when focusing.
 14. A zoom lens according to claim13, wherein said aperture stop is located between said third lens groupand said fourth lens group.
 15. A zoom lens according to claim 11,wherein said aperture stop is located between said third lens group andsaid fourth lens group.
 16. A zoom lens according to claim 15, whereinsaid aperture stop is designed so as to move together with said fourthlens group as the zoom lens positional state changes.
 17. A zoom lensaccording to claim 16 satisfying the condition

    0.75<|f.sub.6 |/f.sub.5 <1.50

wherein f₆ is the focal length of said negative lens subgroup, and f₅ isthe focal length of said fifth lens group.
 18. A zoom lens according toclaim 11, wherein the location of said aperture stop is fixed,regardless of any change in the zoom lens positional state.
 19. A zoomlens according to claim 11 satisfying the condition

    -0.2<(f.sub.4 -f.sub.5)/(f.sub.4 +f.sub.5)<0.2

wherein f₄ is the focal length of said fourth lens group, and f₅ is thefocal length of said fifth lens group.
 20. A zoom lens according toclaim 19 satisfying the condition

    2.5<f.sub.1 /|f.sub.2 |<3.5

wherein f₁ is the focal length of said first lens group, and f₂ is thefocal length of said second lens group.
 21. A zoom lens according toclaim 20 satisfying the condition

    -0.5<(f.sub.2 -f.sub.3)/(f.sub.2 +f.sub.3)<0

wherein f₃ is the focal length of said third lens group.
 22. A zoom lenscapable of forming an image of an object and zooming between a maximumwide-angle state and a maximum telephoto state, the zoom lens comprisingobjectwise to imagewise:a) a first lens group having overall positiverefractive power and a most objectwise lens surface; b) a second lensgroup having overall negative refractive power and separated from saidfirst lens group by a first air space; c) a third lens group havingoverall negative refractive power and separated from said second lensgroup by a second air space; d) a fourth lens group having overallpositive refractive power, a most objectwise lens surface, and separatedfrom said third lens group by a third air space; e) a fifth lens grouphaving positive refractive power and separated from said fourth lensgroup by a fourth air space; and f) wherein the zoom lens is designedsuch that when zooming from the maximum wide-angle state to the maximumtelephoto state, said first lens group and said fourth lens group arefixed in position, and said second lens group and said third lens groupmove imagewise so as to increase said second air space, and said fifthlens group moves objectwise.
 23. A zoom lens according to claim 22,further including:a) a sixth lens group arranged imagewise of said fifthlens group and separated from said fifth lens group by a fifth airspace, the zoom lens designed such that said sixth lens group movesaxially while said fifth air space is changed as the lens positionalstate changes; and b) an aperture stop located between said third lensgroup and said fourth lens group.
 24. A zoom lens according to claim 23satisfying the condition

    1.0<f.sub.1 /(f.sub.w ·f.sub.t).sup.1/2 <1.8

wherein f₁ is the focal length of said first lens group, f_(t) is thefocal length of the zoom lens in the maximum telephoto state, and f_(w)is the focal length of the zoom lens in the maximum wide-angle state.25. A zoom lens according to claim 24 satisfying the condition

    1.5<M.sub.1 /M.sub.4 <2

wherein M₁ is the axial distance from said most objectwise lens surfaceof said first lens group to an image plane, and M₄ is the axial distancefrom said most objectwise lens surface of said fourth lens group to theimage plane.
 26. A zoom lens according to claim 22, wherein said thirdlens group is designed so as to be axially moveable for the purpose offocusing.